2016 Volume 64 Issue 8 Pages 1190-1195
1β,3β,25-Dihydroxy-19-norvitamin D3 (4a) and 1α,3α,25-dihydroxy-19-norvitamin D3 (4b) were synthesized by employing a new A-ring synthon, (1R,3S)-3-((tert-butyldimethylsilyl)oxy)-5-oxocyclohexyl benzoate (19), which was derived from D-(−)-quinic acid in 12 steps. The A-ring was coupled with the circular dichroism (CD) ring by means of Julia–Kocienski olefination to construct the diene unit. The structures of the products were confirmed by 1H-NMR and nuclear Overhauser effect (NOE) experiments.
1α,25-Dihydroxyvitamin D3 (2, Fig. 1; also known as calcitriol), which is the hormonally active form of vitamin D3 (1) in mammalians, regulates calcium and phosphorus homeostasis,1–3) and also has antiproliferative, cell differentiation-inducing and immune-regulatory activities.1,4–6) It is used to treat hyperproliferative disorders, but its clinical utility is limited by side effects such as hypercalcemia and hypercalciuria, which are induced at clinically effective doses. Hence, there is a need for structural development to separate these biological activities.7–11)
19-Norvitamin D3 (3) was first reported by DeLuca and colleagues in 1990,12) and has a characteristic biological activity profile, exhibiting high differentiation potency towards various malignant tissues with a substantially reduced calcemic effect.13) Since then, there have been many synthetic studies of 3, mainly focusing on the A-ring synthon.14,15) We recently reported a new synthetic strategy.16) We are particularly interested in structural derivatization involving the C1 and C3 hydroxy groups, whose geometries are believed to be crucial for antiproliferative activity.17,18) Herein, we described syntheses of 1β,3β,25-dihydroxy-19-norvitamin D3 (4a) and 1α,3α,25-dihydroxy-19-norvitamin D3 (4b), using a newly developed methodology to obtain the 1,3-cis-type A-ring synthon 19.
Synthetic methodologies for 1,3-trans-19-nor type vitamin D derivatives are well developed, but to our knowledge, there is no report of the synthesis of 1,3-cis type 19-nor analogues or their A-ring synthons. As we were interested in synthesizing 1,3-cis type analogues, we decided to investigate Julia–Kocienski olefination as a means to obtain two diastereomers at the same time, namely 1β,3β,25-dihydroxy-19-norvitamin D3 (4a) and 1α,3α,25-dihydroxy-19-norvitamin D3 (4b) (Chart 1). However, because of the structural similarity and similar polarity of these compounds, separation, and structural identification could be challenging.
Synthesis of ketone 6 is illustrated in Chart 2. 1,3,5-Cyclohexanetriol (7) was reacted with the phenylboronic acid in toluene under reflux to give the boronate, whose free hydroxy group was then protected as benzoate ester by reaction with benzoyl chloride in the presence of triethylamine, affording 8 in 76% yield (2 steps).19,20) The boronate ester in 8 was hydrolyzed using pinacol in the presence of BF3·Et2O, and the free hydroxy groups were protected as tert-butyldimethylsilyl (TBS) ether using TBS chloride in the presence of triethylamine and tetrabutylammonium bromide (TBAB), affording 9 in 52% yield. After hydrolysis of benzoyl group in 9 with sodium hydroxide in methanol, the resulting hydroxy group was oxidized with pyridinium chlorochromate (PCC) to give ketone 6 in 56% yield.
With ketone 6 in hand, the CD ring synthon 521–23) and ketone 6 were coupled using lithium bis(trimethylsilyl)amide (LiHMDS) in tetrahydrofuran (THF)24,25) to give 10 in 98% yield as a 1 : 1 mixture of diastereomers 10a and b (Chart 3). However, separation of these two diastereomers was difficult. Moreover, the chemical shifts of 1H at C1 and C3 of these two isomers 10a and b overlapped (δ=3.6–3.9 ppm), and structural identification of these isomers was problematic. Therefore, we decided to modify the hydroxy protecting groups at the A-ring in order to obtain products with different polarity, which would be more easily separable.
Specifically, we planned to change one silyl ether to benzoate ester in ketone 6 to obtain 19. The strongly electron-withdrawing nature of the benzoyl group would make the adjacent C1–H more deshielded than its C3 counterpart, which should enable an easy identification of both H’s in 1H-NMR. This group was also expected to induce some polarity difference between the two target compounds, enabling us to separate them easily on a preparative scale. Thus, we attempted selective deprotection of one TBS group in 6 using tetrabutylammonium fluoride (TBAF) (1 eq) or hydrogen fluoride·pyridine (HF·Py) (1 eq). However, β-elimination and subsequent aromatization reaction took place to generate 12 and 13, respectively (Chart 4). These results led us to develop a new route to synthesize an A-ring synthon with different hydroxy protecting groups at the C1 and C3 positions (19).
We started our synthesis of 19 from 14, which can be obtained from D-(−)-quinic acid in five steps12) (Chart 5). The diol in 14 was protected with benzaldehyde dimethylacetal to give acetal 15 in 82% yield. We found that selective deprotection of one TBS group in 15 proceeded upon slow addition of TBAF in THF (1 M in THF, 1 eq) at 0°C to give a mixture of four stereoisomers 16 in 70% yield. This mixture of isomers was oxidized with tetra-n-propylammonium perruthenate-N-methylmorpholine N-oxide (TPAP-NMO) to give ketone 17 (a mixture of four isomers). Various conditions were investigated for the stereoselective reduction of ketone 17 to 1,3-cis alcohol 18. Among them, diisobutylaluminium hydride (DIBAL)-H in the presence of ZnCl226) was effective, and 1,3-cis alcohol 18 (more polar) was obtained in 67% yield, together with 1,3-trans alcohol 16 (less polar, 29%) after silica gel column separation.
After protection of the hydroxy group in 18 as benzoate by reaction with benzoyl chloride and triethylamine, deprotection of benzylidene acetal under hydrogenation conditions in the presence of palladium hydroxide followed by oxidative cleavage of the resulting diol with NaIO4 aqueous solution in methanol afforded ketone 19. Coupling reaction of CD-ring synthon 5 with ketone 19 was performed to give 20a and b. These two diastereomers were separable by silica gel column chromatography, affording 20a and b in 36 and 35% yield, respectively. The structures of these isomers were confirmed by 1H-NMR and nuclear Overhauser effect correlated spectroscopy (NOESY)27) (Chart 6).
These isomers were converted to 1,3-cis-19-nor vitamin D3 4a and b in 56 and 59% yield, respectively, by reaction with potassium carbonate in methanol–THF followed by deprotection of silyl ethers with HF·Py.
In conclusion, synthesis of 1,3-cis-19-nor type A-ring synthon from 1,3,5-cyclohexanetriol was problematic due to the difficulty of separation and identification of the 1,3-cis-19-norvitamin D3 isomers 4a and b. A simple strategic modification to protect one hydroxy group with benzoate afforded A-ring synthon 19. Finally, 4a and b were synthesized by Julia–Kocienski olefination of this A-ring synthon and a circular dichroism (CD) ring synthon, thus opening up a new route that should be available to build a library of 1,3 modified 1,3-cis-19-nor type vitamin D derivatives in a convergent manner.
All reactions have been carried out in dry solvents, and under inert atmosphere unless otherwise mentioned. Reagents were purchased from Sigma-Aldrich (St. Louis, MO, U.S.A.), TCI and Wako Pure Chemical Industries, Ltd. (Osaka, Japan). Flash chromatography was performed on silica gel 60 (spherical, particle size 40–100 mm; Kanto (Tokyo, Japan)). 1H-NMR spectra have been recorded in deuteriochloroform at 300 and 400 MHz using JMTC 300 and JNM-ECX 400 spectrometers, whereas 13C-NMR spectra have been recorded at 75 and 100 MHz using same spectrometers. The spectra are referenced internally according to residual solvent signal of CDCl3 (1H-NMR: δ=7.26 ppm; 13C-NMR: δ=77.0 ppm). Data for 1H-NMR are recorded as follows: chemical shift (δ ppm), multiplicity (s=singlet; d=doublet; t=triplet; q=quartet; m=multiplet; br=broad), coupling constant (Hz), and integration. Data for 13C-NMR are reported in terms of chemical shift (δ ppm). For mixture of diastereomers NMR of single pure diastereomer or the peaks for major isomers is reported, in other cases diastereomeric protons have been reported in italics. Mass spectra were recorded on a JMS-T100X (JEOL) spectrometer in electrospray ionization (ESI)-MS mode using methanol as solvent.
(1R,5S)-3-Phenyl-2,4-dioxa-3-borabicyclo[3.3.1]nonan-7-yl Benzoate (8)1,3,5-Cyclohexanetriol (3.0 g, 22.69 mmol) was dissolved in toluene (250 mL) under argon, and the mixture was refluxed for 6 h, when no left over starting material was found at TLC, the reaction was cooled to room temperature and the solvent was evaporated under reduced pressure, the white solid left behind was the boronate ester (4.95 g, quant.). The boronate ester (1 g, 4.58 mmol) was then dissolved in pyridine (15 mL) at room temperature, then benzoyl chloride (0.51 mL, 0.62 g, 4.41 mmol) was added, and the mixture was allowed to stir for 12 h at room temperature. After the reaction was finished, pyridine was evaporated off under reduced pressure, the residue was dissolved in benzene and was filtered. The filtrates were concentrated in vacuo and dried under high vacuum for 12 h. Then, it was dissolved in minimum amount of benzene at 80°C and was allowed to cool down gradually overnight, the solids were filtered out and washed with hexane to give 8 (1.12g, 76%).
(3R,5S)-3,5-Bis[(tert-butyldimethylsilyl)oxy]cyclohexyl Benzoate (9)Compound 8 (500 mg, 1.55 mmol) was first dissolved in CH2Cl2 (15 mL), at room temperature, under argon, then pinacol (365 mg, 3.0 mmol) was added followed by BF3·OEt2 (32 mL, 0.77 mmol). This mixture was stirred for 4 h at room temperature, then the solvent was evaporated off under reduced pressure, the left over gum was dissolved in methanol and evaporated under reduced pressure, this process was repeated for five times, and then the left over sticky substance was treated as the crude for the next step. The crude product was dissolved in N,N-dimethylformamide (DMF) (15.5 mL) at 0°C. To the mixture was added tetrabutyl ammonium bromide (48 mg, 0.15 mmol), N,N-dimethyl-4-aminopyridine (DMAP) (189 mg, 1.55 mmol), and TBSCl (2.34 g, 15.5 mmol), then triethylamine (0.59 mL, 434 mg, 4.27 mmol) was added dropwise, after the addition was over the reaction was raised at room temperature, and allowed to stand at room temperature for 15 h. After the reaction was finished, water (75 mL) was added to the reaction, and then the aqueous layer was extracted with CH2Cl2 for three times. The combined organic layer was washed with water for three times, and then was washed with brine, dried over MgSO4, filtered and evaporated in vacuo. The residue was purified by silica gel column (5% ethyl acetate–hexanes) to give 9 (372 mg, 2 steps 52%).
Spectral Data for 91H-NMR (300 MHz, CDCl3) δ: 7.60–7.33 (5H, m), 5.06–4.89 (1H, m), 3.74–3.63 (2H, m), 2.27–2.04 (3H, m), 1.66–1.39 (3H, m), 0.87 (18H, s), 0.06 (12H, s); 13C-NMR (75 MHz, CDCl3) δ: 165.98, 134.83, 133.06, 131.3, 130.64, 129.68, 70.75, 68.62, 66.29, 45.85, 40.89, 25.90, 18.30, −4.54. High resolution (HR)-MS ESI: m/z: Calcd for C25H44Na1O4Si2: 487.2676 [M+Na]+. Found: 487.2658.
(3R,5S)-3,5-Bis[(tert-butyldimethylsilyl)oxy]cyclohexanone (6)To a solution of 9 (500 mg, 1.08 mmol) in CH2Cl2 (22 mL) was added a solution of NaOH (260 mg, 6.5 mmol) in MeOH (44 mL), dropwise at 0°C. The resulting mixture was allowed to stand overnight, the reaction was quenched with 1 M HCl solution, the aqueous layer was washed with CH2Cl2 twice, the combined organic layer was washed with water, followed by brine, dried over MgSO4, filtered and evaporated under reduced pressure. The residue was dissolved in CH2Cl2 (11 mL), and to the solution was added NaOAc (44 mg, 0.54 mmol) and PCC (395 mg 1.87 mmol) at 0°C and the resulting mixture was stirred for 15 min. The reaction mixture was filtered through a pad of Celite, the filtrates were washed with saturated Na2S2O3 solution, the aqueous layer was extracted with CH2Cl2. The combined organic layer was washed with brine, dried over MgSO4, filtered and evaporated in vacuo. The residue was purified on silica gel column (2% ethyl acetate–hexanes) to give ketone 6 (217 mg, 2 steps 56%).
Spectral Data for 61H-NMR (300 MHz, CDCl3) δ: 3.83–3.73 (2H, m), 2.56–2.50 (1H, dd, J=5.2, 14.1 Hz), 2.38–2.30 (2H, t, J=11.0 Hz), 2.29–2.22 (1H, m), 1.82–1.71 (1H, dd, J=11.0, 12.7 Hz), 0.86 (18H, s), 0.06 (12H, s); 13C-NMR (75 MHz, CDCl3) δ: 207.67, 66.85, 51.00, 45.11, 25.81, 18.13, −4.68. HR-MS ESI: m/z: Calcd for C18H38Na1O3Si1: 381.2257 [M+Na]+. Found: 381.2298.
{[(7S,9S)-2-Phenyl-1,3-dioxaspiro[4.5]decane-7,9-diyl]bis(oxy)}bis(tert-butyldimethylsilane) (15)To a solution of 14 (2.53 g, 6.47 mmol) in CH2Cl2 (64.7 mL) was added activated 4Α molecular sieves (3.23 g), benzaldehyde dimethyl acetal (1.24 mL, 1.27 g, 8.41 mmol), and the mixture was stirred for 12 h at room temperature. The reaction mixture was filtered through a pad of Celite, the filtrate was washed with water, aqueous layer was extracted with CH2Cl2 for three times. Combined organic layer was washed with water and brine, dried on MgSO4, filtered and evaporated in vacuo. The residue was purified on silica gel column (2% ethyl acetate–hexanes) to give 15 (2.54 g, 82%) as a mixture of two diastereomers.
Spectral Data for 151H-NMR (300 MHz, CDCl3) δ: 7.50–7.46 (2H, m), 7.41–7.34 (3H, m), 5.92 (5.81) (1H, s), 4.26–4.25 (1H, m), 4.08–3.98 (2H, m), 3.92–3.68 (1H, m), 2.28 (2.17) (1H, d, J=11.9 Hz), 1.97–1.84 (3H, m), 1.67–1.59 (1H, m), 1.48–1.34 (1H, m), 0.90 (18H, d, J=5.9 Hz), 0.1–0.05 (12H, q, J=6.4 Hz); 13C-NMR (75 MHz, CDCl3) δ: 138.71 (138.11), 129.29 (129.15), 128.43, 126.79 (126.58), 102.57 (101.49), 81.52 (80.99), 75.29, 67.38 (67.16), 66.09 (65.83), 46.34 (44.42), 42.73 (42.68), 41.89 (41.80), 25.99, 25.89, 18.27, 18.05, −4.54, −4.83. HR-MS ESI: m/z: Calcd for C26H46Na1O4Si2: 501.2832 [M+Na]+. Found: 501.2805.
(7S,9S)-9-[(tert-Butyldimethylsilyl)oxy]-2-phenyl-1,3-dioxaspiro[4.5]decan-7-ol (16)To a solution of 15 (1.15 g, 2.4 mmol) in THF (48 mL) was added TBAF (1 M in THF, 2.4 mL, 2.4 mmol) at 0°C dropwise over 1 h. The reaction was monitored by TLC carefully. At the point of polar bis-TBS deprotected spot appearance on TLC, the reaction was quenched with saturated NH4Cl. The aqueous layer was extracted with ethyl acetate for three times, and the combined organic layer was washed with water, followed by brine, dried over MgSO4, filtered and evaporated in vacuo. The residue was chromatographed on silica gel column (10–15% ethyl acetate–hexanes) to give 16 as four diastereomers mixtures (399 mg, 70%, br sm).
Spectral Data for 161H-NMR (300 MHz, CDCl3) δ: 7.50–7.46 (2H, m), 7.40–7.36 (3H, m), 5.85 (1H, s), 4.34–4.26 (1H, m), 4.17–4.08 (1H, m), 4.02 (1H, d, J=8.6 Hz), 3.80 (1H, d, J=8.9 Hz), 2.07 (1H, dd, J=3.4, 13.4, Hz), 2.00–1.66 (5H, m), 0.89 (9H, s), 0.09 (6H, s); 13C-NMR (75 MHz, CDCl3) δ: 137.63, 129.56, 128.52, 126.73, 103.22, 82.46, 67.20, 65.11, 44.29, 42.31, 40.06, 25.43, 18.19, −4.69, −4.73. HR-MS ESI: m/z: Calcd for C20H32Na1O4Si1: 387.1976 [M+Na]+. Found: 387.1994.
(R)-9-[(tert-Butyldimethylsilyl)oxy]-2-phenyl-1,3-dioxaspiro[4.5]decan-7-one (17)To a solution of alcohol 16 (410 mg, 1.1 mmol) in CH2Cl2 (11 mL) was added activated molecular sieves (553 mg) and N-methylmorpholene-N-oxide (322 mg, 2.75 mmol) at 0°C under argon. After stirring for 30 min, TPAP (39 mg, 0.11 mmol) was added to the mixture, and the resulting mixture was stirred at 0°C for another 3 h. The reaction mixture was filtered through a short silica gel column (6–8% ethyl acetate–hexanes) to give 17 (407 mg, 99%).
Spectral Data for 171H-NMR (300 MHz, CDCl3) δ: 7.46–7.42 (2H, m), 7.39–7.35 (3H, m), 5.88 (1H, s), 4.39–4.31 (1H, m), 4.00 (1H, d, J=8.6 Hz), 3.78 (1H, d, J=8.6 Hz), 2.69–2.60 (3H, m), 2.43–2.31 (2H, m), 2.03–1.96 (1H, m), 0.87 (9H, s), 0.05 (6H, s); 13C-NMR (75 MHz, CDCl3) δ: 206.06, 137.78, 129.46, 128.50, 126.55, 103.25, 81.18, 75.25, 66.86, 50.16, 49.75, 43.54, 25.83, 18.10, −4.78, −4.82. HR-MS ESI: m/z: Calcd for C20H30Na1O4Si1: 385.1811 [M+Na]+. Found: 385.1851.
(7R,9S)-9-[(tert-Butyldimethylsilyl)oxy]-2-phenyl-1,3-dioxaspiro[4.5]decan-7-ol (18)To a mixture of ketone 17 (400 mg, 1.1 mmol) and ZnCl2 (300 mg, 2.2 mmol) in CH2Cl2 (11 mL) was added DIBAL-H (4.4 mL, 1 M in toluene) at −78°C dropwise, and the resulting mixture was stirred at −78°C for 12 h. To the reaction mixture was added MeOH (3 mL) at −78°C, and the resultant mixture was warmed to room temperature. Then, saturated Rochelle salt solution (5.2 mL) was added, and allowed to stir for 30 min. The aqueous layer was extracted with CH2Cl2 for three times. The combined organic layer was washed with saturated Rochelle salt and brine, dried over MgSO4, filtered, and concentrated in vacuo. The residue was chromatographed on silica gel column (6–8, 9–10% ethyl acetate–hexanes) to give trans alcohols 16 (less polar, 115 mg, 29%) and cis alcohols 18 (more polar, 226 mg, 67%).
Spectral Data for 181H-NMR (300 MHz, CDCl3) δ: 7.48–7.44 (2H, m), 7.41–7.32 (3H, m), 5.85 (1H, s), 4.13–4.02 (3H, m), 3.85 (1H, d, J=8.3 Hz), 2.13–2.00 (3H, m), 1.64–1.43 (3H, m), 0.89 (9H, s), 0.07 (6H, s); 13C-NMR (75 MHz, CDCl3) δ: 137.91, 129.47, 128.49, 126.79, 103.35, 80.40, 67.35, 66.71, 44.36, 42.91, 42.34, 25.94, 18.19, −4.69, −4.76. HR-MS ESI: m/z: Calcd for C20H32Na1O4Si1: 387.1966 [M+Na]+. Found: 387.1994.
(1R,3S)-3-[(tert-Butyldimethylsilyl)oxy]-5-oxocyclohexyl Benzoate (19)To a solution of cis alcohols 18 (219 mg, 0.6 mmol) in CH2Cl2 (5 mL) was added benzoyl chloride (0.15 mL, 186 mg, 1.32 mmol), triethylamine (0.24 mL, 182 mg, 1.8 mmol), and DMAP (102 mg, 0.84 mmol) at room temperature under argon, and the resultant mixture was stirred for 4 h. To the reaction mixture was added saturated NH4Cl, and the aqueous layer was extracted with CH2Cl2 for three times. Combined extracts were washed with water and brine, dried over MgSO4, filtered and concentrated in vacuo. The residue was chromatographed on the silica gel column (5% ethyl acetate–hexanes) to give benzoate-protected cis alcohols (264 mg, 94%). The mixture of benzoate-protected cis alcohols (264 mg, 0.564 mmol) was dissolved in THF (6 mL) under argon, and 10% Pd(OH)2 (26 mg) was added, then argon was purged with hydrogen gas, and the reaction mixture was allowed to stir under the hydrogen atmosphere for 8 h. The reaction mixture was filtered through a pad of Celite, and filtrates were concentrated in vacuo. The residue was dissolved in MeOH (28 mL), and a saturated aqueous solution of NaIO4 (542 mg, 2.53 mmol, in 0.28 mL H2O) was added, the resulting mixture was stirred for 3 h. To the reaction mixture was added water, and aqueous layer was extracted with ethyl acetate until no product was found in the aqueous layer, on TLC. The extracts were washed with brine, dried over MgSO4, filtered and concentrated in vacuo. The residue was chromatographed on silica gel column (2% ethyl acetate–hexanes) to give ketone 19 (158 mg, 64%).
Spectral Data for 191H-NMR (400 MHz, CDCl3) δ: 8.01 (2H, d, J=8.2 Hz), 7.54 (1H, t, J=7.3 Hz), 7.42 (2H, t, J=7.8 Hz), 5.29–5.22 (1H, m), 4.12–4.05 (1H, m), 2.81 (1H, dd, J=5.5, 13.5 Hz), 2.64 (1H, dd, J=5.0, 15.2 Hz), 2.59–2.53 (1H, m), 2.48–2.42 (2H, m), 2.08–2.00 (1H, m), 0.83 (9H, s), 0.03 (6H, s); 13C-NMR (100 MHz, CDCl3) δ: 205.67, 165.66, 133.27, 129.69, 129.78, 128.45, 68.15, 66.34, 50.61, 46.30, 39.50, 25.77, 18.07, −4.77, −4.71. HR-MS ESI: m/z: Calcd for C19H28Na1O4Si: 371.1655 [M+Na]+. Found: 371.1655.
(1S,3R,E)-3-[(tert-Butyldimethylsilyl)oxy]-5-[(E)-2-[(1R,7aR)-7a-methyl-1-[(R)-6-methyl-6-[(triethylsilyl)oxy]heptan-2-yl]hexahydro-1H-inden-4(2H)-ylidene]ethylidene]cyclohexyl Benzoate (20a) and (1R,3S,E)-3-[(tert-Butyldimethylsilyl)oxy]-5-[(E)-2-[(1R,7aR)-7a-methyl-1-[(R)-6-methyl-6-[(triethylsilyl)oxy]heptan-2-yl]hexahydro-1H-inden-4(2H)-ylidene]ethylidene]cyclohexyl Benzoate (20b)To a mixture of CD-ring synthon 5 (36 mg, 59 µmol) and ketone 19 (14 mg, 39 µmol) in THF (0.6 mL) was added LiHMDS (79 µL, 78 µmol) was slowly at −78°C under argon, and the mixture was stirred for 2.5 h, then the mixture was raised at room temperature and allowed to stand for 10 min. To the reaction mixture was added water, and extracted with ether for three times. The combined extracts were washed with brine, dried over MgSO4, filtered and concentrated in vacuo. The residue was passed through a small silica gel column to give 20 as two diastereomer’s mixture (35 mg, 72%). These diastereomers were separated on a silica gel column (0.3% ether–hexane) to give 20a (18 mg, 36%) and 20b (17 mg, 35%).
Spectral Data for 20a1H-NMR (400 MHz, CDCl3) δ: 8.05 (2H, d, J=6.9 Hz), 7.55 (1H, t, J=7.3 Hz), 7.44 (2H, t, J=7.8 Hz), 6.26 (1H, d, J=10.9 Hz), 5.80 (1H, d, J=11.5 Hz), 4.91–4.90 (1H, m), 3.71–3.67 (1H, m), 3.13 (1H, dd, J=4.6, 12.8 Hz), 2.80 (1H, d, J=11.5 Hz), 2.45 (1H, dd, J=4.6, 13.1 Hz), 2.36 (1H, m), 2.14 (1H, t, J=11.9 Hz), 2.02–1.86 (3H, m), 1.67–1.60 (4H, m), 1.41–1.24 (13H, m), 1.17 (6H, s), 0.96–0.82 (22H, m), 0.58–0.52 (9H, m), 0.07 (6H, d, J=6.9 Hz); 13C-NMR (100 MHz, CDCl3) δ: 165.98, 143.35, 132.99, 130.65, 130.23, 129.72, 128.42, 123.05, 115.57, 73.59, 70.49, 68.76, 56.73, 56.46, 46.45, 45.94, 45.62, 41.85, 40.62, 36.55, 36.22, 33.74, 30.11, 29.93, 28.97, 27.73, 25.95, 23.59, 22.39, 20.94, 18.92, 18.21, 12.26, 7.24, 6.91, −4.48, −4.54. HR-MS ESI: m/z: Calcd for C45H76Na1O4Si2: 759.5180 [M+Na]+. Found: 759.5205.
Spectral Data for 20b1H-NMR (400 MHz, CDCl3) δ: 8.04 (2H, d, J=7.3 Hz), 7.55 (1H, t, J=7.8 Hz), 7.44 (2H, t, J=7.8 Hz), 6.29 (1H, d, J=10.9 Hz), 5.84 (1H, d, J=11.5 Hz), 4.91–4.88 (1H, m), 3.62–3.58 (1H, m), 2.99 (1H, dd, J=4.6, 10.9 Hz), 2.79 (1H, d, J=12.4 Hz), 2.66 (1H, dd, J=4.6, 12.4 Hz), 2.37–2.34 (1H, br), 2.25–2.20 (1H, t, J=11.5 Hz), 2.02–1.66 (9H, m), 1.43–1.30 (7H, m), 1.19 (6H, s), 0.96–0.83 (23H, m), 0.59–0.53 (9H, m), 0.09–0.07 (6H, d, J=8.2 Hz); 13C-NMR (100 MHz, CDCl3) δ: 165.96, 143.38, 132.96, 130.62, 130.38, 129.68, 128.39, 123.05, 115.54, 73.56, 71.04, 68.60, 56.73, 56.41, 45.84, 45.61, 42.07, 41.76, 40.56, 38.32, 36.53, 36.23, 30.09, 29.92, 29.79, 28.99, 27.78, 25.96, 23.63, 22.23, 20.93, 18.91, 18.29, 12.15, 7.22, 6.89, −4.59, −4.67. HR-MS ESI: m/z: Calcd for C45H76Na1O4Si2: 759.5180 [M+Na]+. Found: 759.5170.
(1R,3S,E)-5-[(E)-2-[(1R,7aR)-1-[(R)-6-Hydroxy-6-methylheptan-2-yl]-7a-methylhexahydro-1H-inden-4(2H)-ylidene]ethylidene]cyclohexane-1,3-diol (4a)To a solution of 20a (18 mg, 24 µmol) in MeOH (0.6 mL) and THF (2.4 mL) was added K2CO3 (5 mg, 36 µmol) at room temperature under argon, and the mixture was stirred overnight. To the reaction mixture was added saturated NH4Cl, and aqueous layer was extracted with ethyl acetate for three times. The combined organic layer was washed with water and brine, dried over MgSO4, filtered and concentrated in vacuo. The residue was purified by silica gel column (10% ethyl acetate–hexanes) to give alcohol, which was then dissolved in THF (1 mL), and HF·Py (181 mg, 0.16 mL, 6.3 mmol) was added, and the resulting mixture was stirred for 24 h at room temperature. To the reaction mixture was added saturated Na2S2O3, and aqueous layer was extracted with ethyl acetate for three times. The extracts were washed with water and brine, dried over MgSO4, filtered and concentrated in vacuo. The residue was first eluted using 3% MeOH–CH2Cl2 on a silica gel column, and then again purified on a preparative TLC plate using 5% MeOH–CH2Cl2 as the mobile phase to give 4a (5 mg, 56%).
Spectral Data for 4a1H-NMR (400 MHz, CDCl3) δ: 6.23 (1H, d, J=10.9 Hz), 5.86 (1H, d, J=11.5 Hz), 3.91 (2H, m), 2.82 (1H, dd, J=10.3, 4.1 Hz), 2.59 (1H, dd, J=11.5, 3.7 Hz), 2.49 (1H, dd, J=13.3, 3.7 Hz), 2.43–2.38 (1H, m), 2.28–2.23 (1H, m), 2.13–1.24 (27H, m), 1.22 (6H, s), 0.94 (3H, d, J=6.4 Hz), 0.55 (3H, s); 13C-NMR (100 MHz, CDCl3) δ: 142.89, 130.21, 123.82, 115.48, 71.22, 68.92, 68.65, 56.61, 56.41, 45.87, 45.23, 44.50, 41.33, 40.59, 36.95, 36.48, 36.18, 29.46, 29.28, 28.99, 27.75, 23.57, 22.37, 20.89, 18.89, 12.16. HR-MS ESI: m/z: Calcd for C26H44Na1O3: 427.3188 [M+Na]+. Found: 427.3172.
(1R,3S,Z)-5-[(E)-2-[(1R,7aR)-1-[(R)-6-Hydroxy-6-methylheptan-2-yl]-7a-methylhexahydro-1H-inden-4(2H)-ylidene]ethylidene]cyclohexane-1,3-diol (4b)Similar to 20a, compound 20b (17 mg, 24 µmol) in MeOH (0.6 mL) and THF (2.4 mL) was added K2CO3 (4.9 mg, 36 µmol) at room temperature under argon, and the mixture was stirred overnight. To the reaction mixture was added saturated NH4Cl, and aqueous layer was extracted with ethyl acetate for three times. The combined organic layer was washed with water and brine, dried over MgSO4, filtered and concentrated in vacuo. The residue was purified by silica gel column (10% ethyl acetate–hexanes) to give alcohol, which was then dissolved in THF (1 mL), and HF·Py (0.16 mL) was added, and the resulting mixture was stirred for 24 h at room temperature. To the reaction mixture was added saturated Na2S2O3, and aqueous layer was extracted with ethyl acetate. The extracts were washed with water and brine, dried over MgSO4, filtered and concentrated in vacuo. The residue was first eluted using 3% MeOH–CH2Cl2 on a silica gel column, and then again purified on a preparative TLC plate using 5% MeOH–CH2Cl2 as the mobile phase to give 4b (5.5 mg, 59%).
Spectral Data for 4b1H-NMR (400 MHz, CDCl3) δ: 6.34 (1H, d, J=10.9 Hz), 5.87 (1H, d, J=11.5 Hz), 4.01 (2H, br), 2.83 (1H, dd, J=4.6, 10.3 Hz), 2.58 (1H, dd, J=6.4, 13.5 Hz), 2.32–2.24 (3H, m), 2.04–1.97 (3H, m), 1.91–1.84 (2H, m), 1.72–1.21 (23H, m), 0.94 (3H, d, J=6.4 Hz), 0.55 (3H, s); 13C-NMR (100 MHz, CDCl3) δ: 142.89, 130.05, 124.14, 115.44, 71.22, 68.96, 68.77, 56.58, 56.39, 45.85, 45.14, 44.50, 40.56, 40.36, 36.76, 36.47, 36.20, 29.44, 29.31, 29.02, 27.78, 23.60, 22.37, 20.90, 18,89, 12.17. HR-MS ESI: m/z: Calcd for C26H44Na1O3: 427.3188 [M+Na]+. Found: 427.3196.
The authors declare no conflict of interest.
