Practical Synthesis of Pachastrissamine (Jaspine B), 2-epi-Pachastrissamine, and the 2-epi-Pyrrolidine Analogue

Abstract

The practical syntheses of pachastrissamine (jaspine B), 2-epi-pachastrissamine, and the 2-epimer of the pyrrolidine analogue were accomplished via the stereoselective reduction of an allylketone derived from commercially available diethyl D-tartrate and the cross-metathesis of an allyltetrahydrofuran or allypyrrolidine with 1-tridecene as key steps.

Pachastrissamine (1), also known as jaspine B, was first isolated from the Okinawan marine sponge Pachastrissa sp. by Higa and colleagues in 2002¹⁾ and shortly thereafter from a different sponge, Jaspis sp., by Debitus and colleagues in 2003²⁾ (Fig. 1). It is a naturally occurring, novel anhydrophytosphingosine derivative that contains an all-cis-2,3,4-trisubstituted tetrahydrofuran ring with the (2S,3S,4S) absolute configuration and exhibits cytotoxic activity against various human cancer cell lines.^1–9) Recently, Delgado and colleagues reported that 1 causes autophagy mediated by dihydroceramides in human A549 lung cancer cells.⁶⁾ Andrieu-Abadie and colleagues also reported that 1 induces apoptosis in murine B16 melanoma cells through an increase in intracellular ceramide levels resulting from inhibition of the activity of sphingomyelin synthase.^7,8) Moreover, 1 was demonstrated to inhibit several kinases such as sphingosine kinase (SphK), cyclin-dependent kinase 2, and extracellular regulatory kinase.^9,10) Because of its novel structural features and impressive biological activity, many total syntheses of 1 have been accomplished.^{3–7,11–30)} The stereoisomers of 1 have also been synthesized,^{5,6,20–29,31–40)} and their biological activity investigated. Interestingly, the 2-epimer 2^{6,20–26,32,35)} exhibits higher subtype selectivity for sphingosine kinases than 1 and its stereoisomers.¹⁰⁾ Several pachastrissamine analogues have also been synthesized.^7,41–46) Among them, the pyrrolidine analogue 3 was found to have better pharmacological properties than 1.⁴³⁾ This difference in activity may be because of the fact that 3 can exist in multiple ionized forms. In addition, the amino group of the pyrrolidine moiety of 3 can act both as a hydrogen-bond acceptor and as a donor. Despite the high potential of pyrrolidine analogues as new drug candidates, stereoisomers such as the 2-epimer 4 have not yet been synthesized. We previously reported the enantioselective total synthesis of 1 via Sharpless asymmetric dihydroxylation and dirhodium(II)-catalyzed C–H amination as key steps.³⁰⁾ However, this route is not suitable for scalable synthesis because of the low yield of the dirhodium(II)-catalyzed C–H amination reaction. Herein, we report the practical syntheses of pachastrissamine (1), 2-epi-pachastrissamine (2), and the 2-epimer of the pyrrolidine analogue (4) from commercially available diethyl D-tartrate (14).

Fig. 1. Structures of Pachastrissamine (Jaspine B, 1), 2-epi-Pachastrissamine (2), Pyrrolidine Analogue 3, and 2-epi-Pyrrolidine Analogue 4

Results and Discussion

Synthesis of Pachastrissamine (1) and 2-epi-Pachastrissamine (2)

Our retrosynthetic analysis for 1 and 2 is shown in Chart 1. We envisioned that allyltetrahydrofuran 5 would be a key intermediate to introduce the alkyl side-chain moiety via an olefin cross-metathesis reaction. Late-stage introduction of the side-chain makes it easy to synthesize derivatives bearing various side chains at the C-2 position.^7,16,27) To construct the cyclic structure of 5, we planned to employ cyclization of monotosylate 7. Compound 7 would be obtained from 1,2,4-triol 9 via selective tosylation of the primary alcohols catalyzed by dibutyltin oxide (Bu₂SnO).⁴⁷⁾ Triol 9 would be derived from 3,4-syn-homoallylic alcohol 11. The synthesis of 11 would be accomplished via the stereoselective introduction of an allyl group into aldehyde 13, which is readily prepared from commercially available diethyl D-tartrate (14) according to the literature.⁴⁸⁾ In addition, 2-epimer 2 would be synthesized from 3,4-anti-isomer 12 using a procedure similar to that for the synthesis of 1.

Chart 1. Retrosynthetic Analysis of 1 and 2

Our syntheses began with diethyl D-tartrate (14) (Chart 2). Aldehyde 13 was obtained from 14 according to the reported procedure.⁴⁸⁾ Because only 3,4-syn selective alkylation of a similar aldehyde was known,⁴⁹⁾ allylketone 16 was chosen for stereoselective preparation of 11 and 12. Thus, 13 was reacted with allylmagnesium bromide to provide a 1 : 1 mixture of diastereomeric homoallylic alcohols 15 in 76% yield. However, due to the low reproducibility of the reaction, we examined an indium-mediated allylation,⁵⁰⁾ because indium is known to promote chelation-controlled allylation.⁵¹⁾ When aldehyde 13 was treated with indium metal and allyl bromide in the presence of tetrabutylammonium iodide (TBAI) in N,N-dimethylformamide (DMF), 15 was obtained in 83% yield with high reproducibility but no stereoselectivity (1 : 1). Therefore, we next examined the stereoselective reduction⁵²⁾ of allylketone 16 with various reducing reagents (Table 1). Dess–Martin oxidation of 15 generated 16 in quantitative yield. When 16 was reduced with NaBH₄, diisobutylaluminum hydride (DIBAL-H), or sodium bis(2-methoxyethoxy)aluminum hydride (Red-Al), the diastereomeric homoallylic alcohols 11 and 12 were obtained in high yields, but with low stereoselectivity (entries 1–3). Conversely, lithium tri-sec-butylborohydride (L-selectride)⁵³⁾ and zinc borohydride [Zn(BH₄)₂]⁵⁴⁾ gave satisfactory results. When 16 was treated with L-selectride in anhydrous tetrahydrofuran (THF) at −78°C to room temperature for 2 h, 3,4-syn-homoallylic alcohol 11 was obtained as a single stereoisomer in 98% yield (entry 4). In contrast, the use of Zn(BH₄)₂ in a mixture of anhydrous Et₂O and CH₂Cl₂ at −78 to 0°C for 5 h produced 3,4-anti-homoallylic alcohol 12 as the major isomer in 84% yield (entry 5). The observed stereoselectivity can be rationalized, as shown in Fig. 2.⁵²⁾ The syn-selectivity of the reduction with L-selectride is likely because of attack of the hydride on the Re face of Felkin–Anh model A to afford 11. In the case of Zn(BH₄)₂, the hydride likely attacks on the Si face of the chelation model B to produce 12.

Chart 2. Synthesis of Allylic Ketone 16

Reagents and conditions: (a) allyl bromide, In, Bu₄NI, DMF, 0°C to r.t., 3 h, 83%; (b) Dess–Martin periodinane, CH₂Cl₂, 0°C to r.t., 0.5 h, 99%.

Table 1. Stereoselective Reduction of Allylic Ketone 16

Entry	Conditions	Yield (%)	11 : 12a)
1	NaBH4 (2 eq), MeOH, 0°C, 0.5 h	95	1.9 : 1
2	DIBAL-H (2 eq), THF, −78 to −40°C, 1 h	99	1 : 1.3
3	Red-Al (1.8 eq), CH2Cl2, −78 to 0°C, 1.5 h	84	1 : 1.4
4	L-Selectride (2.5 eq), THF, −78°C to r.t., 2 h	98	>99 : 1
5	Zn(BH4)2 (2 eq), CH2Cl2–Et2O (2 : 3), −78 to 0°C, 5 h	84	1 : 8

a) Determined via ¹H-NMR analysis of the crude mixture.

Fig. 2. Stereochemical Preferences for the Stereoselective Reduction of 16 with L-Selectride and Zn(BH₄)₂

With homoallylic alcohols 11 and 12 selectively in hand, we examined the synthesis of 1 and 2 (Chart 3). Removal of the diol protecting group in 3,4-syn-isomer 11 with aqueous sulfuric acid afforded 1,2,4-triol 9 in 76% yield. Tetrahydrofuran ring formation was then investigated. Nkambule and colleagues reported that Bu₂SnO-catalyzed tosylation of 2,4-syn-1,2,4-triols gave the corresponding tetrahydrofurans via selective tosylation of the primary alcohols followed by cyclization, whereas 2,4-anti-1,2,4-triols afforded monotosylates without cyclization.⁵⁵⁾ When triol 9 was treated with tosyl chloride (TsCl) and triethylamine (Et₃N) in the presence of a catalytic amount of Bu₂SnO in CH₂Cl₂ under reflux, tosylation and subsequent cyclization of 7 proceeded in one-pot to afford allyltetrahydrofuran 5 in 84% yield as expected. Next, S_N2 amination was accomplished by reacting 5 first with triflic anhydride (Tf₂O) and pyridine in CH₂Cl₂ and then benzylamine (BnNH₂) at 50°C to produce amine 17 in 67% yield.⁵⁶⁾ Late-stage introduction of the long side chain was achieved via olefin cross-metathesis of 17 using a ruthenium–carbene complex. When allylamine 17 was treated with 4 eq. of 1-tridecene in the presence of Grubbs 2nd generation catalyst in CH₂Cl₂ under reflux for 8 h, (E)-alkene 18 was obtained in 58% yield, along with 18% of isomerized alkene 19.⁵⁷⁾ Catalytic hydrogenation of a mixture of 18 and 19 in the presence of trifluoroacetic acid (TFA) and subsequent treatment with base successfully afforded pachastrissamine 1, [α]_D²⁶ +18.0 (c=0.18, EtOH) {lit.¹⁾ [α]_D +18.0 (c=0.1, EtOH), lit.²¹⁾ [α]_D²⁵ +14.8 (c=0.57, EtOH)}, in 76% yield. Spectroscopic data for 1 were identical to those of the reported sample.²¹⁾ We next examined the synthesis of 2-epi-pachastrissamine (2) from 3,4-anti-isomer 12. Acid treatment of 12 afforded crude 1,2,4-triol 10, which was recrystallized from hexane, and ethyl acetate provided the diastereomerically pure form. Reaction of 2,4-anti-1,2,4-triol 10 with TsCl and Et₃N in the presence of a catalytic amount of Bu₂SnO in CH₂Cl₂ under reflux proceeded smoothly but, surprisingly, afforded tetrahydrofuran 6 in 83% yield. Compound 6 was then converted to 2 via amination and side-chain extension. The synthetic compound 2 was spectroscopically identical to previously synthesized 2,²¹⁾ including its optical rotation ([α]_D²⁶=+18.4 (c=0.39, EtOH); lit.²¹⁾ [α]_D²⁵ +14.5 (c=0.34, EtOH)).

Chart 3. Total Synthesis of Pachastrissamine (1) and 2-epi-Pachastrissamine (2)

Reagents and conditions: (a) 2% H₂SO₄, MeOH, r.t., 24 h, 76%; (b) TsCl, Bu₂SnO, Et₃N, CH₂Cl₂, reflux, 2.5 h, 84%; (c) 1) Tf₂O, pyridine, CH₂Cl₂, −20 to 0°C, 20 min; 2) BnNH₂, 50°C, 19.5 h, 67% (2 steps); (d) 1-tridecene, Grubbs 2nd catalyst, CH₂Cl₂, reflux, 8 h, 18 (58%) and 19 (18%); (e) 1) H₂, Pd(OH)₂–C, TFA, MeOH, r.t., 45 h; 2) NaOH, MeOH, CH₂Cl₂, r.t., 15 min, 76% (2 steps); (f) 2% H₂SO₄, MeOH, r.t., 21.5 h, 84%; (g) TsCl, Bu₂SnO, Et₃N, CH₂Cl₂, reflux, 2.5 h, 83%; (h) 1) Tf₂O, pyridine, CH₂Cl₂, −20 to 0°C, 20 min; 2) BnNH₂, 50°C, 19 h, 76% (2 steps); (i) 1) 1-tridecene, Grubbs 2nd catalyst, CH₂Cl₂, reflux, 17 h; 2) H₂, Pd(OH)₂–C, TFA, MeOH, r.t., 45 h; 3) NaOH, MeOH, CH₂Cl₂, r.t., 15 min, 41% (3 steps).

Synthesis of the 2-Epimer Pyrrolidine Analogue 4

Despite interest in its biological activity, the 2-epimer of the pyrrolidine analogue (4) has not yet been synthesized. Therefore, we next investigated the synthesis of 4 using a similar strategy (Chart 4) involving conversion of 3,4-syn-homoallylic alcohol 11 to 4-(2-nitrobenzenesulfonyl)amino-1,2-diol 20, followed by selective tosylation, cyclization of tosylate 21, extension of the side-chain, and deprotection.

Chart 4. Synthetic Strategy for 4

Based on the above strategy, the synthesis of 4 began with compound 11 (Chart 5). Tosylation of 11 followed by treatment with sodium azide (NaN₃) afforded the corresponding azide in good yield with inversion of configuration at the C-4 position. Reduction of the azide with triphenylphosphine (Ph₃P) in a mixture of THF and water produced amine 23 in 81% yield. Protection of the amino group of 23 with a 2-nitrobenzenesulfonyl (nosyl) group and deprotection of the diol moiety under acidic conditions afforded 4-nosylamino-1,2-diol 20 in high yield. Selective tosylation of the primary hydroxyl group of 20 and subsequent cyclization of tosylate 21 were achieved under the same conditions as described previously to generate the desired allylpyrrolidine 22 in high yield. Triflation of 22 afforded 24, which was treated with BnNH₂ to give amine 25⁵⁸⁾ in 50% yield along with 24% of the eliminated product 26. When olefin cross-metathesis of 25 using 1-tridecene and Grubbs 2nd generation catalyst was performed, alkene 27 was obtained in 80% yield as a mixture of (E)- and (Z)-isomers (E : Z=ca. 7.5 : 1). Removal of the nosyl group from the E/Z mixture of 27 with thiophenol (PhSH) and Cs₂CO₃, and final catalytic hydrogenation in the presence of TFA successfully afforded 4 in good yield after basification.

Chart 5. Synthesis of 2-epi-Pyrrolidine Analogue 4

Reagents and conditions: (a) TsCl, 4-dimethylaminopyridine (DMAP), pyridine, r.t., 48 h, 86%; (b) NaN₃, DMF, 60°C, 24 h, 74%; (c) Ph₃P, THF–H₂O (=20 : 3), 50°C, 24 h, 81%; (d) NsCl, Et₃N, CH₂Cl₂, 0°C to r.t., 1.5 h, 94%; (e) 2% H₂SO₄, MeOH, r.t., 42 h, 81%; (f) TsCl, Bu₂SnO, Et₃N, CH₂Cl₂, reflux, 3 h, 93%; (g) Tf₂O, pyridine, CH₂Cl₂, −20 to 0°C, 20 min; (h) BnNH₂, 50°C, 40 h, 25 (50%) and 26 (24%) (2 steps); (i) 1-tridecene, Grubbs 2nd catalyst, CH₂Cl₂, reflux, 6.5 h, 80% (E/Z=ca. 7.5/1); (j) PhSH, Cs₂CO₃, MeCN, rt to 50°C, 2.5 h, 83%; (k) 1) H₂, Pd(OH)₂–C, TFA, MeOH, r.t., 96 h; 2) NaOH, MeOH, r.t., 15 min, 67% (2 steps).

Conclusion

Practical syntheses of pachastrissamine (1) and 2-epi-pachastrissamine (2) were accomplished. The key intermediates 5 and 6 were respectively obtained via the stereoselective reduction of 16 with L-selectride or Zn(BH₄)₂ followed by monotosylation–cyclization. Subsequent introduction of the amino group, olefin cross-metathesis with 1-tridecene, and catalytic hydrogenation successfully afforded 1 and 2. In addition, the first synthesis of the 2-epimer pyrrolidine analogue 4 was achieved using a similar synthetic strategy. These procedures will be applicable to the synthesis of other derivatives of 1 bearing various alkyl side chains. Biological evaluation of 1, 2, and 4 is currently underway.

Experimental

General

Melting points were determined using a Yanaco micro melting point apparatus and are uncorrected. Optical rotations were determined using a JASCO P-2100 polarimeter. Infrared (IR) spectra were recorded using a JEOL FT/IR-460Plus spectrometer. All NMR spectra were recorded using JEOL ECX-400P or JEOL ECA-500II spectrometers. Proton (¹H)-NMR spectra were recorded at 400 or 500 MHz. Carbon-13 (¹³C)-NMR spectra were recorded using the broadband proton decoupling at 100 or 125 MHz. All chemical shifts, δ, are stated in units of parts per million (ppm), relative to a standard. For ¹H-NMR, the reference point is tetramethylsilane (=0.00 ppm). For ¹³C-NMR, the reference point is CDCl₃ (=77.0 ppm) or CD₃OD (=49.0 ppm). Electron ionization (EI) mass spectra were recorded using a JEOL JMS-GCmate II spectrometer. High resolution FAB mass spectra were recorded using a JEOL JMS-AX 505 spectrometer. Values are reported as a ratio of mass to charge (m/z). Column chromatography was performed on Nacalai Tesque Silica Gel 60 PF₂₅₄ (0.005–0.050 mm), Kanto chemical silica gel 60 N (0.040–0.050 mm) or Merck 9385 silica gel 60 (0.040–0.063 mm). Thin layer chromatography was performed on Merck 5715 silica gel 60 F₂₅₄ or Merck 5554 silica gel 60 F₂₅₄.

(1R,2RS)-1-[(R)-2,2-Diethyl-1,3-dioxolan-4-yl]-1-[(4-methoxybenzyl)oxy]pent-4-en-2-ol (15)

Indium (2.20 g, 19.2 mmol), TBAI (2.36 g, 6.40 mmol) and allyl bromide (1.62 mL, 19.2 mmol) were added to a solution of 13⁴⁸⁾ (1.97 g, 6.40 mmol) in anhydrous DMF (10 mL) at 0°C, and the resulting solution was stirred at room temperature under a nitrogen atmosphere for 3 h. The mixture was treated with sat. aq. NH₄Cl, and then extracted with Et₂O. The organic layer was washed with water and brine, dried over MgSO₄, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–CH₂Cl₂–hexane=3 : 6 : 11) to give 15 (1.86 g, 83%, ca. 1 : 1 mixture of diastereomers) as a colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.89–0.95 (12H, m), 1.62–1.74 (8H, m), 2.21–2.52 (6H, m), 3.35–3.50 (3H, m), 3.62 (1H, t, J=8.2 Hz), 3.68–3.80 (2H, m), 3.805 (3H, s), 3.811 (3H, s), 4.02 (1H, dd, J=8.2, 6.4 Hz), 4.07 (1H, dd, J=7.8, 6.4 Hz), 4.29 (1H, ddd, J=8.2, 6.4, 6.0 Hz), 4.36–4.41 (1H, m), 4.605 (1H, d, J=11.0 Hz), 4.613 (1H, d, J=11.0 Hz), 4.72 (1H, d, J=11.0 Hz), 4.85 (1H, d, J=11.0 Hz), 5.03–5.16 (4H, m), 5.69–5.89 (2H, m), 6.86–6.90 (4H, m), 7.27–7.32 (4H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 8.10, 8.14, 8.2, 8.3, 29.2, 29.4, 29.7, 29.8, 37.9, 39.1, 55.3, 66.6, 66.7, 70.7, 71.4, 73.3, 73.6, 77.6, 78.2, 80.0, 80.5, 113.0, 113.2, 113.76, 113.79, 117.8, 118.0, 129.6, 129.9, 130.38, 130.40, 134.5, 134.7, 159.28, 159.34.

(S)-1-[(R)-2,2-Diethyl-1,3-dioxolan-4-yl]-1-[(4-methoxybenzyl)oxy]pent-4-en-2-one (16)

Dess–Martin periodinane (2.44 g, 5.76 mmol) was added to a solution of 15 (1.35 g, 3.84 mmol) in anhydrous CH₂Cl₂ (38 mL) at 0°C. After stirring at room temperature under a nitrogen atmosphere for 0.5 h, sat. aq. Na₂S₂O₃ was added to the mixture, which was extracted with ether. The organic layer was washed with sat. aq. NaHCO₃, water, and brine; dried over MgSO₄; filtered; and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–hexane=3 : 7) to give 16 (1.32 g, 99%) as a colorless oil. [α]_D²³ −56.6 (c=0.62, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=7.3 Hz), 0.91 (3H, t, J=7.3 Hz), 1.60 (2H, q, J=7.3 Hz), 1.67 (2H, qd, J=7.3, 1.8 Hz), 3.34 (1H, ddt, J=17.9, 6.9, 1.4 Hz), 3.41 (1H, ddt, J=17.9, 6.9, 1.4 Hz), 3.75–3.83 (2H, m), 3.81 (3H, s), 4.00 (1H, dd, J=8.2, 6.9 Hz), 4.25–4.30 (1H, m), 4.55 (1H, d, J=11.5 Hz), 4.64 (1H, d, J=11.5 Hz), 5.10 (1H, dq, J=16.9, 1.4 Hz), 5.18 (1H, dq, J=10.5, 1.4 Hz), 5.88 (1H, ddt, J=16.9, 10.5, 6.9 Hz), 6.87–6.91 (2H, m), 7.26–7.30 (2H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 8.11, 8.14, 28.9, 29.5, 44.4, 55.3, 66.2, 73.3, 83.8, 113.6, 113.9, 118.9, 129.2, 129.7, 130.1, 159.5, 209.5. IR (neat) cm⁻¹: 2973, 2937, 2886, 1718, 1613, 1515, 1464, 1303, 1250, 1173, 1080, 1036, 921, 822. EI-MS m/z: 348.1962 (Calcd for C₂₀H₂₈O₅: 348.1937). MS m/z: 348 (M⁺), 319, 245 (base peak).

(1R,2S)-1-[(R)-2,2-Diethyl-1,3-dioxolan-4-yl]-1-[(4-methoxybenzyl)oxy]pent-4-en-2-ol (11)

L-Selectride (1 M solution in THF, 1.72 mL, 1.72 mmol) was added dropwise to a solution of 16 (239 mg, 0.69 mmol) in anhydrous THF (10 mL) at −78°C under a nitrogen atmosphere. After stirring for 10 min, the resulting solution was allowed to warm to room temperature and stirred for 2 h. The mixture was diluted with EtOAc and then concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–hexane=3 : 17) to give 11 (235 mg, 98%) as a colorless oil. [α]_D¹⁹ +32.1 (c=0.82, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 0.92 (3H, t, J=7.3 Hz), 0.93 (3H, t, J=7.3 Hz), 1.62–1.72 (4H, m), 2.21–2.37 (2H, m), 3.36 (1H, dd, J=6.9, 1.8 Hz), 3.47 (1H, br s), 3.62 (1H, t, J=8.2 Hz), 3.81 (3H, s), 4.07 (1H, dd, J=7.8, 6.0 Hz), 4.36–4.41 (1H, m), 4.61 (1H, d, J=11.0 Hz), 4.85 (1H, d, J=11.0 Hz), 5.03–5.10 (2H, m), 5.74 (1H, ddt, J=16.9, 10.1, 6.9 Hz), 6.87–6.91 (2H, m), 7.28–7.32 (2H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 8.1, 8.3, 29.4, 29.8, 39.1, 55.3, 66.7, 71.4, 73.6, 78.1, 80.0, 113.2, 113.7, 117.8, 129.9, 130.4, 134.5, 159.3. IR (neat) cm⁻¹: 3462 (br), 3075, 2973, 2938, 2881, 1641, 1613, 1586, 1515, 1464, 1378, 1356, 1302, 1250, 1173, 1086, 1037, 921, 822, 759. EI-MS m/z: 350.2082 (Calcd for C₂₀H₃₀O₅: 350.2093). MS m/z: 351 ([M+1]⁺), 350 (M⁺), 321 (base peak).

(1R,2R)-1-[(R)-2,2-Diethyl-1,3-dioxolan-4-yl]-1-[(4-methoxybenzyl)oxy]pent-4-en-2-ol (12)

Zinc borohydride (0.15 M solution in Et₂O, 2.10 mL, 0.32 mmol) was added dropwise to a solution of 16 (56 mg, 0.16 mmol) in anhydrous CH₂Cl₂ (1.6 mL) at −78°C under a nitrogen atmosphere. After stirring at –78°C for 70 min, the resulting solution was allowed to warm to 0°C over a period of 240 min. The mixture was treated with sat. aq. NH₄Cl, and then extracted with EtOAc. The organic layer was washed with brine, dried over MgSO₄, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–CH₂Cl₂–hexane=3 : 6 : 11) to give 12 (47 mg, 84%, 11 : 12=1 : 8) as a colorless oil. Diastereomerically pure 12 was obtained by careful column chromatography. [α]_D¹⁸ +29.8 (c=1.06, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 0.91 (3H, t, J=7.3 Hz), 0.92 (3H, t, J=7.3 Hz), 1.61–1.72 (4H, m), 2.21–2.29 (1H, m), 2.39–2.45 (1H, m), 2.57 (1H, d, J=5.5 Hz), 3.40 (1H, t, J=6.0 Hz), 3.67–3.79 (2H, m), 3.79 (3H, s), 4.01 (1H, dd, J=8.2, 6.4 Hz), 4.25–4.31 (1H, m), 4.60 (1H, d, J=11.0 Hz), 4.72 (1H, d, J=11.0 Hz), 5.10–5.15 (2H, m), 5.78–5.88 (1H, m), 6.85–6.89 (2H, m), 7.26–7.29 (2H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 8.0, 8.1, 29.1, 29.5, 37.9, 55.1, 66.5, 70.6, 73.2, 77.6, 80.5, 112.8, 113.7, 117.9, 129.5, 130.3, 134.7, 159.2. IR (neat) cm⁻¹: 3467 (br), 3074, 2974, 2939, 2882, 1641, 1613, 1586, 1514, 1464, 1377, 1356, 1302, 1250, 1173, 1082, 1036, 920, 822, 738. EI-MS m/z: 350.2102 (Calcd for C₂₀H₃₀O₅: 350.2093). MS m/z: 350 (M⁺), 321, 264, 176 (base peak).

(2R,3R,4S)-3-[(4-Methoxybenzyl)oxy]hept-6-ene-1,2,4-triol (9)

Diluted H₂SO₄ (2%, 0.45 mL) was added to a solution of 11 (158 mg, 0.45 mmol) in MeOH (4.5 mL) at room temperature and the resulting solution was stirred for 24 h. Potassium carbonate (311 mg, 2.25 mmol) was added to the mixture at 0°C. After stirring for 0.5 h, the resulting mixture was dried over MgSO₄, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: MeOH–CH₂Cl₂=3 : 97) to give 9 (96 mg, 76%) as a colorless crystalline solid. mp 77–78°C (from EtOAc–hexane). [α]_D²³ +2.5 (c=0.22, MeOH). ¹H-NMR (400 MHz, CDCl₃) δ: 2.28–2.45 (3H, m), 2.81 (1H, d, J=6.4 Hz), 2.88–2.91 (1H, m), 3.47 (1H, dd, J=4.6, 2.8 Hz), 3.59–3.65 (1H, m), 3.77–3.88 (3H, m), 3.81 (3H, s), 4.60 (2H, s), 5.09–5.14 (2H, m), 5.82 (1H, ddt, J=16.9, 10.1, 6.9 Hz), 6.88–6.91 (2H, m), 7.25–7.28 (2H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 39.0, 55.3, 62.2, 69.9, 70.5, 74.1, 79.7, 114.0, 118.1, 129.7, 129.9, 134.4, 159.6. IR (KBr) cm⁻¹: 3303 (br), 3237 (br), 3076, 2945, 2916, 2876, 2836, 1641, 1614, 1587, 1515, 1440, 1350, 1305, 1250, 1181, 1134, 1092, 1062, 1037, 999, 971, 913, 878, 844, 822, 725. EI-MS m/z: 282.1474 (Calcd for C₁₅H₂₂O₅: 282.1467). MS m/z: 282 (M⁺), 221, 164 (base peak).

(3R,4S,5S)-5-Allyl-4-[(4-methoxybenzyl)oxy]tetrahydrofuran-3-ol (5)

p-Toluenesulfonyl chloride (117 mg, 0.61 mmol), Bu₂SnO (6.9 mg, 0.028 mmol), and Et₃N (0.17 mL, 1.22 mmol) were added to a solution of 9 (157 mg, 0.56 mmol) in anhydrous CH₂Cl₂ (6 mL) under a nitrogen atmosphere. After heating under reflux with stirring for 2.5 h, the mixture was cooled to room temperature, treated with sat. aq. NH₄Cl, and extracted with EtOAc. The organic layer was washed with water and brine, dried over MgSO₄, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–hexane=2 : 3) to give 5 (123 mg, 84%) as a colorless oil. [α]_D²² +25.4 (c=0.61, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 1.76 (1H, br s), 2.37–2.50 (2H, m), 3.63 (1H, dd, J=9.6, 1.8 Hz), 3.75 (1H, dd, J=4.1, 0.9 Hz), 3.81 (3H, s), 4.07 (1H, td, J=6.9, 3.7 Hz), 4.16 (1H, dd, J=9.6, 4.6 Hz), 4.33–4.35 (1H, m), 4.47 (1H, d, J=11.5 Hz), 4.59 (1H, d, J=11.5 Hz), 5.04–5.08 (1H, m), 5.13 (1H, dq, J=16.9, 1.8 Hz), 5.82 (1H, ddt, J=16.9, 10.1, 6.9 Hz), 6.87–6.90 (2H, m), 7.24–7.28 (2H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 33.3, 55.3, 71.8, 73.5, 75.2, 80.0, 84.1, 113.8, 116.9, 129.3, 130.0, 135.0, 159.3. IR (neat) cm⁻¹: 3407 (br), 3076, 3001, 2935, 2874, 2838, 1642, 1613, 1586, 1514, 1465, 1442, 1395, 1345, 1303, 1250, 1174, 1089, 1036, 971, 918, 822, 740. EI-MS m/z: 264.1357 (Calcd for C₁₅H₂₀O₄: 264.1362). MS m/z: 264 (M⁺, base peak).

(3S,4S,5S)-5-Allyl-N-benzyl-4-[(4-methoxybenzyl)oxy]tetrahydrofuran-3-amine (17)

Triflic anhydride (0.09 mL, 0.55 mmol) was added dropwise to a solution of 5 (96 mg, 0.36 mmol) and pyridine (0.06 mL, 0.73 mmol) in anhydrous CH₂Cl₂ (1.5 mL) at −20°C. After stirring at 0°C under nitrogen atmosphere for 20 min, the resulting mixture was diluted with CH₂Cl₂ and washed with cold 1 M HCl, sat. aq. NaHCO₃, water, and brine. The organic layer was dried over MgSO₄, filtered, and concentrated under reduced pressure to produce triflate (155 mg) as a crude mixture. Benzylamine (1.1 mL) was added to this crude mixture and the resulting solution was stirred for 19.5 h at 50°C. The mixture was purified by silica gel column chromatography (eluent: EtOAc–hexane=1 : 1) to give 17 (86 mg, 67%) as a brown oil. [α]_D²² −42.5 (c=0.93, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 1.75 (1H, br s), 2.40–2.55 (2H, m), 3.42 (1H, td, J=8.2, 4.6 Hz), 3.57 (1H, t, J=8.7 Hz), 3.68 (2H, s), 3.80 (3H, s), 3.91–3.97 (3H, m), 4.50 (1H, d, J=11.0 Hz), 4.66 (1H, d, J=11.0 Hz), 5.06–5.10 (1H, m), 5.14 (1H, dq, J=17.4, 1.8 Hz), 5.85 (1H, ddt, J=17.4, 10.1, 6.9 Hz), 6.85–6.88 (2H, m), 7.22–7.33 (7H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 34.6, 52.4, 55.3, 61.1, 70.5, 74.0, 77.9, 81.6, 113.9, 116.8, 127.0, 127.9, 128.4, 129.5, 130.2, 135.3, 140.2, 159.4. IR (neat) cm⁻¹: 2925, 2851, 1640, 1612, 1583, 1514, 1455, 1302, 1249, 1174, 1112, 1083, 1068, 1034, 914, 821, 737, 700. EI-MS m/z: 353.1985 (Calcd for C₂₂H₂₇NO₃: 353.1991). MS m/z: 353 (M⁺), 352 ([M−1]⁺), 231 (base peak).

(3S,4S,5S)-N-Benzyl-4-(4-methoxybenzyloxy)-5-[(E)-tetradec-2-en-1-yl]tetrahydrofuran-3-amine (18) and (3S,4S,5S)-N-Benzyl-4-(4-methoxybenzyloxy)-5-[(E)-tetradec-1-en-1-yl]tetrahydrofuran-3-amine (19)

Grubbs 2nd generation catalyst (31 mg, 0.037 mmol) and 1-tridecene (0.17 mL, 0.74 mmol) were added to a solution of 17 (65 mg, 0.18 mmol) in anhydrous CH₂Cl₂ (2 mL) under a nitrogen atmosphere. After heating under reflux with stirring for 8 h, the resulting mixture was cooled to room temperature and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–CH₂Cl₂–hexane=3 : 2 : 5) to give 18 (54 mg, 58%) and 19 (17 mg, 18%).

18: Brown oil. [α]_D²² −23.6 (c=1.50, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 0.88 (3H, t, J=6.9 Hz), 1.25–1.36 (19H, m), 1.97–2.02 (2H, m), 2.39–2.44 (2H, m), 3.41 (1H, td, J=8.7, 4.6 Hz), 3.55 (1H, t, J=8.7 Hz), 3.66 (1H, d, J=13.7 Hz), 3.68 (1H, d, J=13.7 Hz), 3.80 (3H, s), 3.85–3.91 (2H, m), 3.96 (1H, t, J=7.8 Hz), 4.49 (1H, d, J=11.0 Hz), 4.67 (1H, d, J=11.0 Hz), 5.41 (1H, dt, J=15.1, 6.9 Hz), 5.53 (1H, dt, J=15.1, 6.9 Hz), 6.85–6.88 (2H, m), 7.22–7.33 (7H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 14.1, 22.7, 29.2, 29.3, 29.47, 29.52, 29.6, 29.7, 31.9, 32.7, 33.3, 52.4, 55.2, 61.2, 70.5, 74.0, 77.7, 82.3, 113.8, 126.1, 127.0, 127.9, 128.3, 129.5, 130.3, 133.1, 140.2, 159.3. IR (neat) cm⁻¹: 2925, 2853, 1613, 1586, 1514, 1456, 1343, 1302, 1249, 1173, 1112, 1066, 1037, 970, 822, 735, 699. EI-MS m/z: 507.3705 (Calcd for C₃₃H₄₉NO₃: 507.3712). MS m/z: 507 (M⁺), 386 (base peak).

19: Brown oil. [α]_D²² −13.2 (c=0.49, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.24–1.43 (21H, m), 2.05–2.11 (2H, m), 3.41 (1H, ddd, J=9.2, 7.8, 4.6 Hz), 3.58 (1H, t, J=8.7 Hz), 3.62 (1H, d, J=12.8 Hz), 3.65 (1H, d, J=12.8 Hz), 3.80 (3H, s), 3.88 (1H, br t, J=4.1 Hz), 3.98 (1H, t, J=7.8 Hz), 4.31 (1H, dd, J=7.8, 3.2 Hz), 4.36 (1H, d, J=11.0 Hz), 4.67 (1H, d, J=11.0 Hz), 5.70 (1H, dd, J=15.6, 7.8 Hz), 5.78 (1H, dt, J=15.6, 6.4 Hz), 6.85–6.88 (2H, m), 7.22–7.33 (7H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 14.1, 22.7, 29.0, 29.29, 29.34, 29.5, 29.60, 29.63, 29.7, 31.9, 32.5, 52.3, 55.3, 61.3, 70.5, 73.4, 78.6, 83.4, 113.8, 126.4, 127.0, 128.0, 128.4, 129.6, 130.2, 135.3, 140.2, 159.3. IR (neat) cm⁻¹: 2925, 2853, 1613, 1514, 1464, 1343, 1301, 1249, 1214, 1173, 1110, 1060, 1036, 974, 822, 750, 695. EI-MS m/z: 507.3690 (Calcd for C₃₃H₄₉NO₃: 507.3712). MS m/z: 507 (M⁺), 493, 372, 288, 162, 150 (base peak).

(2S,3S,4S)-4-Amino-2-tetradecyltetrahydrofuran-3-ol (1, Pachastrissamine)

Trifluoroacetic acid (0.20 mL, 2.78 mmol) and 20% palladium hydroxide on carbon (14 mg) were added to a solution of alkene mixture of 18 and 19 (47 mg, 0.093 mmol, 18 : 19=ca. 3.4 : 1) in anhydrous MeOH (2 mL) and the resulting solution was stirred at room temperature under a hydrogen atmosphere (1 atm) for 45 h. After completion of the reaction (checked by TLC), the mixture was filtered through a pad of celite and concentrated under reduced pressure to give TFA salt of pachastrissamine as a crude mixture, which was dissolved in anhydrous CH₂Cl₂ (1.6 mL). Methanolic NaOH (2.5 M, 1.6 mL) was added to this mixture at room temperature. After stirring for 15 min, the mixture was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: MeOH–CHCl₃–NH₄OH=10 : 100 : 1) to give 1 (21 mg, 76% from alkene mixture) as a colorless solid. mp 90–91°C [lit.²¹⁾ mp 95–97°C, lit.⁵⁹⁾ mp 90–92°C, lit.⁶⁰⁾ mp 89–91°C]. [α]_D²⁶ +18.0 (c=0.18, EtOH) [lit.¹⁾ [α]_D +18.0 (c=0.1, EtOH), lit.²¹⁾ [α]_D²⁵ +14.8 (c=0.57, EtOH)]. ¹H-NMR (400 MHz, CDCl₃) δ: 0.88 (3H, t, J=6.9 Hz), 1.25–1.47 (24H, m), 1.59–1.73 (2H, m), 2.08 (2H, br s), 3.51 (1H, dd, J=8.2, 6.9 Hz), 3.65 (1H, ddd, J=7.3, 6.9, 5.0 Hz), 3.74 (1H, ddd, J=7.3, 6.4, 3.7 Hz), 3.87 (1H, dd, J=5.0, 3.7 Hz), 3.92 (1H, dd, J=8.2, 7.3 Hz). ¹³C-NMR (100 MHz, CDCl₃) δ: 14.1, 22.7, 26.3, 29.3, 29.4, 29.6, 29.7, 29.8, 31.9, 54.3, 71.7, 72.3, 83.2. IR (KBr) cm⁻¹: 3386 (br), 3341, 3285, 2955, 2920, 2850, 1691, 1584, 1544, 1469, 1380, 1352, 1151, 1119, 1091, 1069, 1037, 988, 848, 720. EI-MS m/z: 299.2831 (Calcd for C₁₈H₃₇NO₂: 299.2824). MS m/z: 299 (M⁺, base peak).

(2R,3R,4R)-3-[(4-Methoxybenzyl)oxy]hept-6-ene-1,2,4-triol (10)

Diluted H₂SO₄ (2%, 1.6 mL) was added to a solution of 12 (560 mg, 1.60 mmol) in MeOH (16 mL) at room temperature and the resulting solution was stirred for 21.5 h. Potassium carbonate (1.10 g, 8.00 mmol) was added to the mixture at 0°C. After stirring for 0.5 h, the resulting mixture was dried over MgSO₄, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: MeOH–CH₂Cl₂=3 : 97) to give 10 (379 mg, 84%) as a colorless crystalline solid. mp 62–63°C (from EtOAc–hexane). [α]_D²⁶ −8.0 (c=0.45, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 2.25–2.33 (1H, m), 2.37–2.49 (2H, m), 2.79 (1H, br dd, J=4.6, 3.2 Hz), 3.17 (1H, br d, J=6.9 Hz), 3.41 (1H, dd, J=6.0, 3.2 Hz), 3.64 (1H, ddd, J=11.0, 7.8, 4.6 Hz), 3.72 (1H, ddd, J=11.0, 6.0, 4.6 Hz), 3.81 (3H, s), 3.90–3.98 (2H, m), 4.51 (1H, d, J=11.0 Hz), 4.63 (1H, d, J=11.0 Hz), 5.14–5.20 (2H, m), 5.78–5.88 (1H, m), 6.87–6.91 (2H, m), 7.24–7.28 (2H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 38.2, 55.3, 64.1, 70.9, 71.3, 72.7, 79.7, 114.0, 118.6, 129.5, 129.8, 134.3, 159.6. IR (KBr) cm⁻¹: 3408 (br), 3303 (br), 3073, 2995, 2974, 2945, 2924, 2877, 2834, 1640, 1616, 1589, 1519, 1472, 1466, 1454, 1441, 1394, 1320, 1305, 1293, 1254, 1218, 1182, 1131, 1088, 1067, 1041, 1012, 912, 874, 820, 748. EI-MS m/z: 282.1461 (Calcd for C₁₅H₂₂O₅: 282.1467). MS m/z: 282 (M⁺, base peak).

(3R,4S,5R)-5-Allyl-4-[(4-methoxybenzyl)oxy]tetrahydrofuran-3-ol (6)

p-Toluenesulfonyl chloride (166 mg, 0.87 mmol), Bu₂SnO (10.0 mg, 0.040 mmol), and Et₃N (0.24 mL, 1.74 mmol) were added to a solution of 10 (224 mg, 0.79 mmol) in anhydrous CH₂Cl₂ (8 mL) under a nitrogen atmosphere. After heating under reflux with stirring for 2.5 h, the mixture was cooled to room temperature, treated with sat. aq. NH₄Cl, and extracted with EtOAc. The organic layer was washed with water and brine, dried over MgSO₄, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–hexane=2 : 3) to give 6 (174 mg, 83%) as a colorless oil. [α]_D²⁵ +38.5 (c=0.54, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 1.74 (1H, br d, J=6.4 Hz), 2.40–2.44 (2H, m), 3.64 (1H, br dt, J=4.1, 1.4 Hz), 3.79–3.83 (1H, m), 3.81 (3H, s), 3.85 (1H, br s), 3.90 (1H, dd, J=10.3, 3.7 Hz), 4.23–4.25 (1H, br m), 4.51 (1H, d, J=11.5 Hz), 4.53 (1H, d, J=11.5 Hz), 5.09–5.16 (2H, m), 5.83 (1H, ddt, J=16.9, 10.1, 6.9 Hz), 6.87–6.91 (2H, m), 7.24–7.28 (2H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 38.0, 55.3, 71.8, 74.0, 76.4, 83.4, 88.7, 113.9, 117.7, 129.5, 129.8, 134.1, 159.4. IR (neat) cm⁻¹: 3420 (br), 3075, 3001, 2932, 2866, 1642, 1613, 1586, 1514, 1464, 1442, 1364, 1336, 1303, 1250, 1175, 1090, 1035, 981, 919, 822, 757. EI-MS m/z: 264.1366 (Calcd for C₁₅H₂₀O₄: 264.1362). MS m/z: 264 (M⁺), 223, 163 (base peak).

(3S,4S,5R)-5-Allyl-N-benzyl-4-[(4-methoxybenzyl)oxy]tetrahydrofuran-3-amine

Triflic anhydride (0.16 mL, 0.99 mmol) was added dropwise to a solution of 6 (174 mg, 0.66 mmol) and pyridine (0.11 mL, 1.32 mmol) in anhydrous CH₂Cl₂ (2.6 mL) at −20°C. After stirring at 0°C under a nitrogen atmosphere for 20 min, the resulting mixture was diluted with CH₂Cl₂ and washed with cold 1 M HCl, sat. aq. NaHCO₃, water, and brine. The organic layer was dried over MgSO₄, filtered, and concentrated under reduced pressure to produce triflate (266 mg) as a crude mixture. Benzylamine (2 mL) was added to this crude mixture and the resulting solution was stirred for 19 h at 50°C. The mixture was purified by silica gel column chromatography (eluent: EtOAc–CHCl₃–hexane=4 : 3 : 3) to give the title compound (177 mg, 76%) as a brown oil. [α]_D²⁶ −6.3 (c=0.96, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 2.22–2.26 (2H, m), 3.22–3.27 (1H, m), 3.57 (1H, t, J=8.2 Hz), 3.63 (1H, dd, J=5.5, 3.2 Hz), 3.70 (1H, d, J=12.8 Hz), 3.73 (1H, d, J=12.8 Hz), 3.81 (3H, s), 3.99 (1H, dd, J=8.2, 6.4 Hz), 4.05 (1H, td, J=6.4, 3.2 Hz), 4.34 (1H, d, J=11.5 Hz), 4.48 (1H, d, J=11.5 Hz), 5.07–5.12 (2H, m), 5.74–5.84 (1H, m), 6.86–6.90 (2H, m), 7.22–7.34 (7H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 38.7, 52.3, 55.3, 59.0, 71.2, 71.4, 79.7, 82.2, 113.8, 117.5, 127.0, 128.1, 128.4, 129.6, 129.9, 134.2, 140.3, 159.4. IR (neat) cm⁻¹: 3335, 3063, 3028, 3000, 2930, 2863, 2834, 1638, 1613, 1586, 1514, 1456, 1362, 1302, 1249, 1173, 1100, 1067, 1034, 916, 822, 748, 700. EI-MS m/z: 353.1984 (Calcd for C₂₂H₂₇NO₃: 353.1991). MS m/z: 353 (M⁺), 232 (base peak).

(2R,3S,4S)-4-Amino-2-tetradecyltetrahydrofuran-3-ol (2,2-epi-Pachastrissamine)

Grubbs 2nd generation catalyst (6 mg, 0.007 mmol) and 1-tridecene (0.14 mL, 0.59 mmol) were added to a solution of (3S,4S,5R)-5-allyl-N-benzyl-4-[(4-methoxybenzyl)oxy]tetrahydrofuran-3-amine (52 mg, 0.15 mmol) in anhydrous CH₂Cl₂ (1.5 mL) under a nitrogen atmosphere. After heating under reflux with stirring for 17 h, the resulting mixture was cooled to room temperature and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–CH₂Cl₂–hexane=3 : 2 : 10) to give an inseparable mixture of (3S,4S,5R)-N-benzyl-4-(4-methoxybenzyloxy)-5-[(E)-tetradec-2-en-1-yl]tetrahydrofuran-3-amine and (3S,4S,5R)-N-benzyl-4-(4-methoxybenzyloxy)-5-[(E)-tetradec-1-en-1-yl]tetrahydrofuran-3-amine (58 mg), which was dissolved in anhydrous MeOH (2 mL). Trifluoroacetic acid (0.25 mL, 3.42 mmol) and 20% palladium hydroxide on carbon (18 mg) were added to this mixture and the resulting solution was stirred at room temperature under a hydrogen atmosphere for 45 h. After completion of the reaction (checked by TLC), the mixture was filtered through a pad of celite and concentrated under reduced pressure to give TFA salt of 2-epi-pachastrissamine as a crude mixture, which was dissolved in anhydrous CH₂Cl₂ (1.9 mL). Methanolic NaOH (2.5 M, 1.9 mL) was added to this mixture at room temperature. After stirring for 15 min, the resulting mixture was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: MeOH–CHCl₃–NH₄OH=10 : 100 : 1) to give 2 (18 mg, 41% from (3S,4S,5R)-5-allyl-N-benzyl-4-[(4-methoxybenzyl)oxy]tetrahydrofuran-3-amine) as a colorless amorphous solid. [α]_D²⁶ +18.4 (c=0.39, EtOH) [lit.²¹⁾ [α]_D²⁵ +14.5 (c=0.34, EtOH)]. ¹H-NMR (400 MHz, CDCl₃) δ: 0.88 (3H, t, J=6.9 Hz), 1.25–1.64 (26H, m), 2.51 (3H, br s), 3.41–3.50 (2H, m), 3.60–3.69 (2H, m), 4.12 (1H, dd, J=8.2, 6.0 Hz). ¹³C-NMR (100 MHz, CDCl₃) δ: 14.1, 22.7, 25.9, 29.3, 29.5, 29.6, 29.7, 31.9, 33.7, 52.6, 73.2, 74.8, 85.2. IR (KBr) cm⁻¹: 3334, 3278, 3138 (br), 2954, 2918, 2851, 1696, 1600, 1471, 1371, 1318, 1124, 1074, 1046, 1036, 997, 986, 966, 914, 718. EI-MS m/z: 299.2817 (Calcd for C₁₈H₃₇NO₂: 299.2824). MS m/z: 299 (M⁺, base peak).

(1R,2S)-1-[(R)-2,2-Diethyl-1,3-dioxolan-4-yl]-1-[(4-methoxybenzyl)oxy]pent-4-en-2-yl 4-Methylbenzenesulfonate

p-Toluenesulfonyl chloride (800 mg, 4.2 mmol) and DMAP (17 mg, 0.14 mmol) were added to a solution of 11 (490 mg, 1.4 mmol) in pyridine (7.4 mL) under a nitrogen atmosphere. After stirring at room temperature for 48 h, the mixture was concentrated under reduced pressure and diluted with EtOAc. The organic layer was washed with sat. aq. NH₄Cl, water, and brine; dried over MgSO₄; filtered; and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–hexane=1 : 9) to give the title compound (608 mg, 86%) as a colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=7.3 Hz), 0.88 (3H, t, J=7.3 Hz), 1.57–1.65 (4H, m), 2.26–2.33 (1H, m), 2.42 (3H, s), 2.57–2.64 (1H, m), 3.51 (1H, dd, J=6.4, 4.1 Hz), 3.54 (1H, t, J=8.2 Hz), 3.81 (3H, s), 3.95 (1H, dd, J=8.2, 6.4 Hz), 4.22 (1H, dt, J=8.2, 6.4 Hz), 4.50–4.54 (1H, m), 4.57 (1H, d, J=11.5 Hz), 4.67 (1H, d, J=11.5 Hz), 4.90–4.98 (2H, m), 5.43 (1H, ddt, J=16.9, 10.1, 6.9 Hz), 6.86–6.89 (2H, m), 7.23–7.28 (4H, m), 7.68–7.72 (2H, m).

(4R)-4-{(1R,2R)-2-Azido-1-[(4-methoxybenzyl)oxy]-4-penten-1-yl}-2,2-dimethyl-1,3-dioxolane

(1R,2S)-1-[(R)-2,2-Diethyl-1,3-dioxolan-4-yl]-1-[(4-methoxybenzyl)oxy]pent-4-en-2-yl 4-methylbenzenesulfonate (608 mg, 1.20 mmol) was dissolved in anhydrous DMF (4.8 mL). Sodium azide (298 mg, 3.6 mmol) was added to the mixture, and the resulting solution was stirred at 60°C under a nitrogen atmosphere for 24 h. The mixture was then cooled to room temperature, treated with water, and extracted with Et₂O. The organic layer was washed with brine, dried over MgSO₄, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: CH₂Cl₂) to give the title compound (334 mg, 74%) as a colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.91 (3H, t, J=7.3 Hz), 0.92 (3H, t, J=7.3 Hz), 1.62–1.71 (4H, m), 2.38–2.54 (2H, m), 3.31 (1H, ddd, J=9.6, 6.0, 3.7 Hz), 3.44 (1H, t, J=6.0 Hz), 3.64 (1H, t, J=8.2 Hz), 3.81 (3H, s), 4.01 (1H, dd, J=8.2, 6.0 Hz), 4.23 (1H, dt, J=8.2, 6.0 Hz), 4.61 (1H, d, J=10.5 Hz), 4.74 (1H, d, J=10.5 Hz), 5.14–5.23 (2H, m), 5.78–5.88 (1H, m), 6.86–6.90 (2H, m), 7.29–7.32 (2H, m).

(4R)-4-{(1R,2R)-2-Amino-1-[(4-methoxybenzyl)oxy]-4-penten-1-yl}-2,2-dimethyl-1,3-dioxolane (23)

(4R)-4-{(1R,2R)-2-Azido-1-[(4-methoxybenzyl)oxy]-4-penten-1-yl}-2,2-dimethyl-1,3-dioxolane (334 mg, 0.89 mmol) was dissolved in a mixture of THF and water (20 : 3, 7.1 mL). Triphenylphosphine (467 mg, 1.78 mmol) was then added to this solution at room temperature. After stirring at 50°C under a nitrogen atmosphere for 24 h, the resulting mixture was cooled to room temperature and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: MeOH–CH₂Cl₂=3 : 97) to give 23 (252 mg, 81%) as a colorless oil. [α]_D¹⁸ +26.9 (c=1.02, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 0.91 (3H, t, J=7.3 Hz), 0.92 (3H, t, J=7.3 Hz), 1.61–1.71 (4H, m), 2.09 (1H, ddd, J=14.2, 9.2, 8.2 Hz), 2.30–2.36 (1H, m), 2.75–2.80 (1H, m), 3.37 (1H, dd, J=6.4, 4.6 Hz), 3.67 (1H, dd, J=8.7, 7.8 Hz), 3.80 (3H, s), 4.00 (1H, dd, J=7.8, 6.4 Hz), 4.28 (1H, dt, J=8.7, 6.4 Hz), 4.58 (1H, d, J=11.0 Hz), 4.77 (1H, d, J=11.0 Hz), 5.07–5.12 (2H, m), 5.71–5.82 (1H, m), 6.86–6.90 (2H, m), 7.28–7.31 (2H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 8.1, 8.3, 29.5, 29.8, 37.9, 52.2, 55.2, 66.6, 73.6, 78.0, 82.6, 112.9, 113.7, 117.7, 129.5, 130.7, 135.7, 159.2. IR (neat) cm⁻¹: 3375, 3074, 2973, 2937, 2881, 1639, 1613, 1586, 1514, 1464, 1442, 1375, 1356, 1338, 1302, 1249, 1199, 1173, 1128, 1080, 1037, 920, 823, 761, 737. EI-MS m/z: 349.2250 (Calcd for C₂₀H₃₁NO₄: 349.2253). MS m/z: 349 (M⁺), 320 (base peak).

(4R)-4-{(1R,2R)-1-[(4-Methoxybenzyl)oxy]-2-[(2-nitrophenyl)sulfonyl]amino-4-penten-1-yl}-2,2-dimethyl-1,3-dioxolane

Nosyl chloride (168 mg, 0.76 mmol) was added to a solution of 23 (252 mg, 0.72 mmol) and Et₃N (0.2 mL, 1.44 mmol) in anhydrous CH₂Cl₂ (2.9 mL) under a nitrogen atmosphere at 0°C. After stirring at room temperature for 1.5 h, the resulting mixture was treated with 1 M HCl and extracted with CH₂Cl₂. The organic layer was washed with sat. aq. NaHCO₃, water and brine; dried over MgSO₄; filtered; and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–hexane=1 : 4) to give the title compound (362 mg, 94%) as a colorless oil. [α]_D²⁰ +24.8 (c=0.96, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 0.84 (3H, t, J=7.3 Hz), 0.91 (3H, t, J=7.3 Hz), 1.61–1.70 (4H, m), 2.23–2.30 (1H, m), 2.42–2.50 (1H, m), 3.36 (1H, t, J=4.1 Hz), 3.68 (1H, dd, J=8.7, 7.8 Hz), 3.78–3.84 (1H, m), 3.81 (3H, s), 3.90 (1H, dd, J=7.8, 6.4 Hz), 4.22 (1H, ddd, J=8.7, 6.4, 4.1 Hz), 4.32 (1H, d, J=11.0 Hz), 4.40 (1H, d, J=11.0 Hz), 4.92–4.95 (1H, m), 5.01 (1H, dq, J=16.9, 1.4 Hz), 5.64 (1H, ddt, J=16.9, 10.1, 6.9 Hz), 6.42 (1H, br d, J=8.2 Hz), 6.81–6.84 (2H, m), 7.09–7.13 (2H, m), 7.57–7.61 (2H, m), 7.79–7.83 (1H, m), 8.06–8.10 (1H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 8.0, 8.1, 29.51, 29.55, 36.7, 55.3, 55.6, 66.2, 72.2, 76.2, 77.1, 113.7, 113.8, 118.3, 125.2, 129.2, 129.6, 130.0, 132.6, 132.9, 133.6, 135.6, 147.4, 159.2. IR (neat) cm⁻¹: 3331, 3077, 2974, 2939, 2880, 1643, 1613, 1587, 1541, 1515, 1464, 1442, 1423, 1360, 1303, 1249, 1171, 1125, 1084, 1059, 1035, 998, 918, 853, 823, 784, 737, 703, 657. EI-MS m/z: 534.2040 (Calcd for C₂₆H₃₄N₂O₈S: 534.2036). MS m/z: 536 ([M+2]⁺), 535 ([M+1]⁺), 534 (M⁺), 517, 505, 431 (base peak).

(2R,3R,4R)-3-[(4-Methoxybenzyl)oxy]-4-[(2-nitrophenyl)sulfonyl]aminohept-6-ene-1,2-diol (20)

Diluted H₂SO₄ (2%, 0.7 mL) was added to a solution of (4R)-4-{(1R,2R)-1-[(4-methoxybenzyl)oxy]-2-[(2-nitrophenyl)sulfonyl]amino-4-penten-1-yl}-2,2-dimethyl-1,3-dioxolane (362 mg, 0.68 mmol) in MeOH (6.8 mL) at room temperature. After stirring for 42 h, K₂CO₃ (470 mg, 3.4 mmol) was added to the resulting solution at 0°C and the mixture was then stirred for 0.5 h. The resulting mixture was dried over MgSO₄, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAC–hexane=1 : 1) to give 20 (257 mg, 81%) as a colorless viscous oil. [α]_D²⁵ −65.4 (c=1.10, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 2.17 (1H, br s), 2.32 (1H, dt, J=14.7, 7.3 Hz), 2.44 (1H, dt, J=14.7, 7.3 Hz), 2.91 (1H, br d, J=7.8 Hz), 3.45–3.50 (2H, m), 3.58 (1H, br dd, J=11.0, 5.0 Hz), 3.80 (3H, s), 3.89–3.95 (2H, m), 4.23 (1H, d, J=11.5 Hz), 4.34 (1H, d, J=11.5 Hz), 4.90–5.04 (2H, m), 5.59 (1H, ddt, J=16.9, 10.1, 6.9 Hz), 6.71 (1H, br d, J=7.8 Hz), 6.82–6.86 (2H, m), 7.08–7.12 (2H, m), 7.62–7.69 (2H, m), 7.83–7.88 (1H, m), 8.13–8.17 (1H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 37.0, 55.1, 55.3, 64.3, 70.4, 71.9, 77.5, 114.0, 118.6, 125.3, 128.8, 129.7, 130.3, 132.8, 133.0, 133.3, 135.6, 147.5, 159.6. IR (neat) cm⁻¹: 3515 (br), 3334 (br), 3078, 3012, 2935, 2839, 1643, 1613, 1587, 1540, 1514, 1466, 1442, 1423, 1361, 1303, 1250, 1168, 1121, 1062, 1034, 1000, 963, 925, 854, 825, 783, 756, 702, 656. EI-MS m/z: 466.1392 (Calcd for C₂₁H₂₆N₂O₈S: 466.1410). MS m/z: 466 (M⁺), 449, 280, 255 (base peak).

(3R,4R,5R)-5-Allyl-4-[(4-methoxybenzyl)oxy]pyrrolidine-3-ol (22)

p-Toluenesulfonyl chloride (115 mg, 0.605 mmol), Bu₂SnO (6.8 mg, 0.028 mmol), and Et₃N (0.17 mL, 1.22 mmol) were added to a solution of 20 (257 mg, 0.55 mmol) in anhydrous CH₂Cl₂ (5.5 mL) under a nitrogen atmosphere. After heating under reflux with stirring for 3 h, the mixture was cooled to room temperature, treated with sat. aq. NH₄Cl and extracted with EtOAc. The organic layer was washed with water and brine, dried over MgSO₄, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–hexane=2 : 3) to give 22 (229 mg, 93%) as a colorless oil. [α]_D¹⁹ −72.4 (c=1.04, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 1.94 (1H, br dd, J=3.7, 2.3 Hz), 2.55–2.71 (2H, m), 3.54 (1H, dd, J=11.0, 2.3 Hz), 3.75 (1H, dd, J=11.0, 5.0 Hz), 3.80 (3H, s), 3.82–3.83 (1H, br m), 4.01 (1H, dd, J=10.5, 4.6 Hz), 4.24–4.27 (1H, br m), 4.30 (1H, d, J=11.5 Hz), 4.37 (1H, d, J=11.5 Hz), 5.10–5.15 (2H, m), 5.74–5.85 (1H, m), 6.79–6.83 (2H, m), 7.02–7.06 (2H, m), 7.52–7.56 (2H, m), 7.60–7.64 (1H, m), 7.97–8.01 (1H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 37.7, 55.29, 55.35, 64.9, 70.7, 74.1, 84.9, 113.7, 118.7, 123.9, 129.2, 129.4, 130.4, 131.2, 131.3, 133.4, 133.9, 148.7, 159.3. IR (neat) cm⁻¹: 3523 (br), 3078, 3006, 2936, 2839, 1640, 1613, 1587, 1545, 1514, 1465, 1441, 1371, 1356, 1302, 1249, 1217, 1169, 1127, 1086, 1034, 925, 851, 822, 774, 758, 743, 729, 656. EI-MS m/z: 448.1320 (Calcd for C₂₁H₂₄N₂O₇S: 448.1304). MS m/z: 450 ([M+2]⁺), 449 ([M+1]⁺), 448 (M⁺), 407 (base peak).

(3S,4S,5R)-5-Allyl-N-benzyl-4-[(4-methoxybenzyl)oxy]-1-[(2-nitrophenyl)sulfonyl]pyrrolidine-3-amine (25)

Triflic anhydride (0.13 mL, 0.77 mmol) was added dropwise to a solution of 22 (229 mg, 0.51 mmol) and pyridine (0.08 mL, 1.02 mmol) in anhydrous CH₂Cl₂ (2 mL) at –20°C. After stirring at 0°C under a nitrogen atmosphere for 20 min, the resulting mixture was diluted with CH₂Cl₂ and washed with cold 1 M HCl, sat. aq. NaHCO₃, water, and brine. The organic layer was dried over MgSO₄, filtered, and concentrated under reduced pressure to produce triflate 24 (293 mg) as a crude mixture. Benzylamine (1.5 mL) was added to this crude mixture and the resulting solution was stirred for 40 h at 50°C. The mixture was purified by silica gel column chromatography (eluent: EtOAc–CH₂Cl₂–hexane=3 : 3 : 4) to give 25 (135 mg, 50%) and eliminated product 26 (51 mg, 24%).

25: Brown oil. [α]_D²⁵ −83.0 (c=0.95, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 1.77 (1H, br s), 2.14–2.22 (1H, m), 2.57–2.63 (1H, m), 3.12 (1H, t, J=9.2 Hz), 3.38–3.43 (1H, m), 3.60 (1H, d, J=13.3 Hz), 3.65 (1H, d, J=13.3 Hz), 3.67 (1H, br d, J=2.8 Hz), 3.72 (1H, dd, J=9.2, 7.3 Hz), 3.80 (3H, s), 4.09–4.13 (1H, m), 4.13 (1H, d, J=11.0 Hz), 4.33 (1H, d, J=11.0 Hz), 5.07–5.13 (2H, m), 5.72–5.82 (1H, m), 6.78–6.81 (2H, m), 6.98–7.01 (2H, m), 7.20–7.32 (5H, m), 7.49–7.53 (2H, m), 7.57–7.61 (1H, m), 7.93–7.95 (1H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 38.8, 51.6, 51.9, 55.3, 57.6, 63.3, 70.4, 78.4, 113.7, 118.7, 123.8, 127.2, 128.0, 128.4, 129.2, 129.4, 130.4, 130.6, 131.1, 133.2, 133.5, 139.7, 148.7, 159.4. IR (neat) cm⁻¹: 3330, 3073, 3027, 3002, 2933, 2867, 2838, 1640, 1612, 1586, 1544, 1514, 1466, 1440, 1373, 1357, 1302, 1249, 1199, 1172, 1127, 1075, 1032, 923, 851, 822, 776, 742, 730, 701, 654. EI-MS m/z: 537.1956 (Calcd for C₂₈H₃₁N₃O₆S: 537.1934). MS m/z: 538 ([M+1]⁺), 537 (M⁺), 519, 416, 401, 282, 148 (base peak).

26: Brown oil. [α]_D²³ −101.9 (c=1.08, CHCl₃). ¹H-NMR (400 MHz, CDCl₃) δ: 2.33–2.41 (1H, m), 2.53–2.60 (1H, m), 3.80 (3H, s), 4.11 (1H, br dd, J=8.7, 3.7 Hz), 4.20 (1H, d, J=11.5 Hz), 4.27 (1H, d, J=11.5 Hz), 4.28–4.30 (1H, m), 5.11–5.16 (2H, m), 5.35 (1H, br t, J=3.7 Hz), 5.75 (1H, ddt, J=16.9, 10.1, 7.3 Hz), 6.68 (1H, d, J=3.7 Hz), 6.79–6.82 (2H, m), 7.00–7.04 (2H, m), 7.54–7.64 (3H, m), 7.90–7.93 (1H, m). ¹³C-NMR (100 MHz, CDCl₃) δ: 37.5, 55.3, 65.1, 69.2, 83.4, 110.9, 113.7, 119.2, 124.0, 129.2, 129.7, 130.1, 130.6, 131.5, 132.2, 133.8, 134.1, 148.6, 159.2. IR (neat) cm⁻¹: 3095, 3003, 2934, 2909, 2839, 1613, 1587, 1545, 1514, 1466, 1440, 1373, 1302, 1250, 1177, 1135, 1055, 1037, 925, 851, 822, 776, 742, 729, 655. FAB-MS m/z: 431.1295 [M+H]⁺ (Calcd for C₂₁H₂₃N₂O₆S: 431.1277). MS m/z: 430 (M⁺), 413, 244, 186, 137, 121 (base peak).

(3S,4S,5R)-N-Benzyl-4-(4-methoxybenzyloxy)-5-[(E)-tetradec-2-en-1-yl]-1-[(2-nitrophenyl)sulfonyl]pyrrolidine-3-amine [(E)-27] and (3S,4S,5R)-N-Benzyl-4-(4-methoxybenzyloxy)-5-[(Z)-tetradec-2-en-1-yl]-1-[(2-nitrophenyl)sulfonyl]pyrrolidine-3-amine [(Z)-27]

Grubbs 2nd generation catalyst (11 mg, 0.013 mmol) and 1-tridecene (0.24 mL, 1.00 mmol) were added to a solution of 25 (135 mg, 0.25 mmol) in anhydrous CH₂Cl₂ (2.5 mL) under a nitrogen atmosphere. After heating under reflux with stirring for 6.5 h, the resulting mixture was cooled to room temperature and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: EtOAc–CH₂Cl₂–hexane=3 : 2 : 5) to give an inseparable mixture of (E)-27 and (Z)-27 (138 mg, 80%, E/Z=ca. 7.5/1) as a brown oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.88 (3H×2, t, J=6.9 Hz, both isomers), 1.25–1.37 (18H×2, m, both isomers), 1.86 (1H×2, br s, both isomers), 1.96–2.23 (3H×2, m, both isomers), 2.50–2.60 (1H×2, m, both isomers), 3.08 (1H, t, J=9.2 Hz, (Z)-isomer), 3.10 (1H, t, J=9.2 Hz, (E)-isomer), 3.38–3.47 (1H×2, m, both isomers), 3.56–3.76 (4H×2, m, both isomers), 3.80 (3H×2, s, both isomers), 4.04–4.17 (2H×2, m, both isomers), 4.32 (1H, d, J=11.5 Hz, (E)-isomer), 4.37 (1H, d, J=11.5 Hz, (Z)-isomer), 5.31–5.38 (1H, m, (Z)-isomer), 5.34 (1H, ddd, J=15.1, 7.8, 6.4 Hz, (E)-isomer), 5.48 (1H, dt, J=15.1, 6.4 Hz, (E)-isomer), 5.54 (1H, dt, J=11.0, 7.3 Hz, (Z)-isomer), 6.78–6.82 (2H×2, m, both isomers), 6.97–7.04 (2H×2, m, both isomers), 7.20–7.32 (5H×2, m, both isomers), 7.48–7.61 (3H×2, m, both isomers), 7.93–7.95 (1H×2, m, both isomers). ¹³C-NMR (125 MHz, CDCl₃) δ: 14.1, 22.7, 27.6, 29.30, 29.36, 29.38, 29.40, 29.58, 29.61, 29.63, 29.66, 29.70, 29.72, 31.9, 32.4, 32.7, 37.6, 51.4, 51.6, 51.8, 51.9, 55.3, 57.6, 57.8, 63.9, 64.1, 70.3, 78.1, 78.2, 113.8, 123.79, 123.83, 124.6, 127.3, 128.0, 128.1, 128.5, 129.28, 129.32, 129.48, 129.53, 130.4, 130.8, 131.1, 133.2, 133.9, 135.2, 139.6, 148.7, 159.4.

(2R,3S,4S)-4-Amino-2-tetradecylpyrrolidine-3-ol (4)

Cesium carbonate (52 mg, 0.16 mmol) and PhSH (0.01 mL, 0.10 mmol) were added to a solution of (E)-27 and (Z)-27 (56 mg, 0.08 mmol, E/Z=ca. 7.5/1) in anhydrous MeCN (3 mL) under a nitrogen atmosphere at room temperature. After stirring at 50°C for 2.5 h, the resulting solution was cooled to room temperature and treated with sat. aq. NaHCO₃. The mixture was extracted with EtOAc and the organic layer was washed with brine, dried over MgSO₄, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: MeOH–CH₂Cl₂=7 : 93) to give the deprotected product (36 mg, 83%) as a colorless oil, which was dissolved in anhydrous MeOH (1.3 mL). Trifluoroacetic acid (0.16 mL, 2.1 mmol) and 20% palladium hydroxide on carbon (11 mg) were added to this mixture and the resulting mixture was stirred at room temperature under a hydrogen atmosphere for 4 d. After completion of the reaction (checked by TLC), the mixture was filtered through a pad of celite and concentrated under reduced pressure to give TFA salt of 4 as a crude mixture, which was dissolved in anhydrous CH₂Cl₂ (1.2 mL). Methanolic NaOH (2.5 M, 1.2 mL) was added to this solution at room temperature. After stirring for 15 min, the mixture was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: MeOH–EtOH–CH₂Cl₂–NH₄OH=6 : 12 : 77 : 5) to give 4 (14 mg, 67%) as a colorless solid. mp 107–108°C. [α]_D²⁵ +13.9 (c=0.31, MeOH). ¹H-NMR (500 MHz, CD₃OD) δ: 0.90 (3H, t, J=6.9 Hz), 1.26–1.49 (26H, m), 1.56–1.65 (1H, br m), 2.64 (1H, dd, J=10.9, 8.0 Hz), 2.92 (1H, br q, J=5.7 Hz), 3.17 (1H, dd, J=10.9, 6.9 Hz), 3.24 (1H, br q, J=6.9 Hz), 3.62–3.68 (1H, m). ¹³C-NMR (100 MHz, CD₃OD) δ: 14.4, 23.7, 28.1, 30.5, 30.70, 30.75, 30.79, 30.9, 33.1, 35.3, 52.3, 54.9, 66.0, 77.5. IR (KBr) cm⁻¹: 3348, 3264 (br), 3240, 2954, 2916, 2848, 1584, 1470, 1456, 1431, 1379, 1351, 1118, 1080, 1031, 1019, 957, 930, 896, 860, 826, 719. EI-MS m/z: 298.2962 (Calcd for C₁₈H₃₈N₂O: 298.2984). MS m/z: 299 ([M+1]⁺), 298 (M⁺), 297 ([M–1]⁺), 281, 240, 226 (base peak).

Conflict of Interest

The authors declare no conflict of interest.

References and Notes

• 1) Kuroda I., Musman M., Ohtani I. I., Ichiba T., Tanaka J., Gravalos D. G., Higa T., J. Nat. Prod., 65, 1505–1506 (2002).
• 2) Ledroit V., Debitus C., Lavaud C., Massiot G., Tetrahedron Lett., 44, 225–228 (2003).
• 3) Liu J., Du Y., Dong X., Meng S., Xiao J., Cheng L., Carbohydr. Res., 341, 2653–2657 (2006).
• 4) Ghosal P., Ajay S., Meena S., Sinha S., Shaw A. K., Tetrahedron Asymmetry, 24, 903–908 (2013) and 24, 1625 (2013).
• 5) Santos C., Fabing I., Saffon N., Ballereau S., Génisson Y., Tetrahedron, 69, 7227–7233 (2013).
• 6) Canals D., Mormeneo D., Fabriàs G., Llebaria A., Casas J., Delgado A., Bioorg. Med. Chem., 17, 235–241 (2009).
• 7) Salma Y., Ballereau S., Maaliki C., Ladeira S., Andrieu-Abadie N., Génisson Y., Org. Biomol. Chem., 8, 3227–3243 (2010).
• 8) Salma Y., Lafont E., Therville N., Carpentier S., Bonnafé M.-J., Levade T., Génisson Y., Andrieu-Abadie N., Biochem. Pharmacol., 78, 477–485 (2009).
• 9) Yoo H., Lee Y. S., Lee S., Kim S., Kim T.-Y., Phytother. Res., 26, 1927–1933 (2012).
• 10) Yoshimitsu Y., Oishi S., Miyagaki J., Inuki S., Ohno H., Fujii N., Bioorg. Med. Chem., 19, 5402–5408 (2011).
• 11) Enders D., Terteryan V., Paleček J., Synthesis, 2008, 2278–2282 (2008).
• 12) Ichikawa Y., Matsunaga K., Masuda T., Kotsuki H., Nakano K., Tetrahedron, 64, 11313–11318 (2008).
• 13) Inuki S., Yoshimitsu Y., Oishi S., Fujii N., Ohno H., Org. Lett., 11, 4478–4481 (2009).
• 14) Urano H., Enomoto M., Kuwahara S., Biosci. Biotechnol. Biochem., 74, 152–157 (2010).
• 15) Vichare P., Chattopadhyay A., Tetrahedron Asymmetry, 21, 1983–1987 (2010).
• 16) Inuki S., Yoshimitsu Y., Oishi S., Fujii N., Ohno H., J. Org. Chem., 75, 3831–3842 (2010).
• 17) Lee H.-J., Lim C., Hwang S., Jeong B.-S., Kim S., Chem. Asian J., 6, 1943–1947 (2011).
• 18) Rao G. S., Rao B. V., Tetrahedron Lett., 52, 6076–6079 (2011).
• 19) Dhand V., Chang S., Britton R., J. Org. Chem., 78, 8208–8213 (2013).
• 20) Abraham E., Davies S. G., Roberts P. M., Russell A. J., Thomson J. E., Tetrahedron Asymmetry, 19, 1027–1047 (2008).
• 21) Yoshimitsu Y., Inuki S., Oishi S., Fujii N., Ohno H., J. Org. Chem., 75, 3843–3846 (2010).
• 22) Llaveria J., Díaz Y., Matheu M. I., Castillón S., Eur. J. Org. Chem., 2011, 1514–1519 (2011).
• 23) Passiniemi M., Koskinen A. M. P., Org. Biomol. Chem., 9, 1774–1783 (2011).
• 24) Bae H., Jeon H., Baek D. J., Lee D., Kim S., Synthesis, 44, 3609–3612 (2012).
• 25) Schmiedel V. M., Stefani S., Reissig H.-U., Beilstein J. Org. Chem., 9, 2564–2569 (2013).
• 26) Jana A. K., Panda G., RSC Adv., 3, 16795–16801 (2013).
• 27) Yoshimitsu Y., Miyagaki J., Oishi S., Fujii N., Ohno H., Tetrahedron, 69, 4211–4220 (2013).
• 28) Lin C.-W., Liu S.-W., Hou D.-R., Org. Biomol. Chem., 11, 5292–5299 (2013).
• 29) Martinková M., Mezeiová E., Fabišíková M., Gonda J., Pilátová M., Mojžiš J., Carbohydr. Res., 402, 6–24 (2015).
• 30) Yakura T., Sato S., Yoshimoto Y., Chem. Pharm. Bull., 55, 1284–1286 (2007).
• 31) Reddipalli G., Venkataiah M., Mishra M. K., Fadnavis N. W., Tetrahedron Asymmetry, 20, 1802–1805 (2009).
• 32) Jayachitra G., Sudhakar N., Anchoori R. K., Rao B. V., Roy S., Banerjee R., Synthesis, 2010, 115–119 (2010).
• 33) Rao G. S., Sudhakar N., Rao B. V., Basha S. J., Tetrahedron Asymmetry, 21, 1963–1970 (2010).
• 34) Prasad K. R., Penchalaiah K., Tetrahedron Asymmetry, 22, 1400–1403 (2011).
• 35) Rao G. S., Rao B. V., Tetrahedron Lett., 52, 4861–4864 (2011).
• 36) Sánchez-Eleuterio A., Quintero L., Sartillo-Piscil F., J. Org. Chem., 76, 5466–5471 (2011).
• 37) Lee D., Synlett, 23, 2840–2844 (2012).
• 38) Martinková M., Pomikalová K., Gonda J., Vilková M., Tetrahedron, 69, 8228–8244 (2013).
• 39) Martinková M., Mezeiová E., Gonda J., Jacková D., Pomikalová K., Tetrahedron Asymmetry, 25, 750–766 (2014).
• 40) Shelke A. M., Rawat V., Sudalai A., Suryavanshi G., RSC Adv., 4, 49770–49774 (2014).
• 41) Chandrasekhar S., Tiwari B., Prakash S. J., ARKIVOC, 2006, 155–161 (2006).
• 42) Génisson Y., Lamandé L., Salma Y., Andrieu-Abadie N., André C., Baltas M., Tetrahedron Asymmetry, 18, 857–864 (2007).
• 43) Rives A., Ladeira S., Levade T., Andrieu-Abadie N., Génisson Y., J. Org. Chem., 75, 7920–7923 (2010).
• 44) Salma Y., Ballereau S., Ladeira S., Lepetit C., Chauvin R., Andrieu-Abadie N., Génisson Y., Tetrahedron, 67, 4253–4262 (2011) and 68, 1819 (2012).
• 45) Jeon H., Bae H., Baek D. J., Kwak Y.-S., Kim D., Kim S., Org. Biomol. Chem., 9, 7237–7242 (2011).
• 46) Kwon Y., Song J., Bae H., Kim W.-J., Lee J.-Y., Han G.-H., Lee S. K., Kim S., Mar. Drugs, 13, 824–837 (2015).
• 47) Martinelli M. J., Vaidyanathan R., Pawlak J. M., Nayyar N. K., Dhokte U. P., Doecke C. W., Zollars L. M. H., Moher E. D., Khau V. V., Košmrlj B., J. Am. Chem. Soc., 124, 3578–3585 (2002).
• 48) Somfai P., Olsson R., Tetrahedron, 49, 6645–6650 (1993).
• 49) Williams D. R., Klingler F. D., Tetrahedron Lett., 28, 869–872 (1987).
• 50) Dhanjee H., Minehan T. G., Tetrahedron Lett., 51, 5609–5612 (2010).
• 51) Nambu H., Noda N., Niu W., Fujiwara T., Yakura T. Asian, J. Org. Chem., 4, 1246–1249 (2015).
• 52) Iida H., Yamazaki N., Kibayashi C., J. Org. Chem., 51, 3769–3771 (1986).
• 53) Lu X., Byun H.-S., Bittman R., J. Org. Chem., 69, 5433–5438 (2004).
• 54) Selvam J. J. P., Rajesh K., Suresh V., Babu D. C., Venkateswarlu Y., Tetrahedron Asymmetry, 20, 1115–1119 (2009).
• 55) Gamedze M. P., Maseko R. B., Chigondo F., Nkambule C. M., Tetrahedron Lett., 53, 5929–5932 (2012).
• 56) Similar S_N2-type amination of the tosyloxy derivative with benzylamine successively proceeded under neat conditions at high temperature.³⁴⁾
• 57) Hanessian S., Giroux S., Larsson A., Org. Lett., 8, 5481–5484 (2006).
• 58) The stereochemistry of 25 was confirmed by nuclear Overhauser effect (NOE) experiment; positive NOE was observed between the allylic-H and C4-H.
• 59) Abraham E., Brock E. A., Candela-Lena J. I., Davies S. G., Georgiou M., Nicholson R. L., Perkins J. H., Roberts P. M., Russell A. J., Sánchez-Fernández E. M., Scott P. M., Smith A. D., Thomson J. E., Org. Biomol. Chem., 6, 1665–1673 (2008).
• 60) van den Berg R. J. B. H. N., Boltje T. J., Verhagen C. P., Litjens R. E. J. N., Van der Marel G. A., Overkleeft H. S., J. Org. Chem., 71, 836–839 (2006).