Efficient N-Acyldopamine Synthesis

Abstract

N-Acyldopamines are endogenous analogs of capsaicin that exhibit cannabinoid-like activities and were identified from brain extracts. Among them, N-arachidonoyldopamine (AADA) and N-oleoyldopamine (ODA) were characterized as transient receptor potential vanilloid type V1 channel (TRPV1) ligands. Recently, it was shown that N-acyldopamines may possess diverse physiological roles in addition to their ligand activities. To study the multiple functions and action mechanisms of endogenous N-acyldopamines, a simple and efficient method of N-acyldopamine synthesis was investigated. The eighteen potentially endogenous N-acyldopamines and two deuterated ones, N-palmitoyl dopamine-d₅ and N-stearoyl dopamine-d₅, were efficiently synthesized without protective groups in CH₂Cl₂ under optimized conditions using propylphosphoric acid cyclic anhydride (PPACA) as a condensation agent.

N-Acyldopamines are members of the endocannabinoids and are present in nervous tissues and exhibit cannabinoid-like activities.¹⁾ N-Arachidonoyldopamine (NADA), an N-acyldopamine, is known as a ligand for the cannabinoid type 1 receptor (CB1), but not CB2, and inhibits the N-arachidonoyl-ethanolamine (AEA) transporter and fatty acid amide hydrolase (FAAH) in the endogenous cannabinoid system.²⁾ In addition, some N-acyldopamines including NADA and N-oleoyldopamine (ODA) act as agonists for the transient receptor potential vanilloid type V1 channel (TRPV1), while N-palmitoyldopamine (PALDA) and N-stearoyldopamine (STEARDA) are nearly inactive as TRPV1 ligands^3–5) (Chart 1). In addition to their ligand activities, recent studies suggest that N-acyldopamines possess diverse biological and pharmacological properties including anti-inflammatory and immunomodulatory activities,^6,7) hypoximimetic activities,⁸⁾ antioxidant and neuroprotective activities,⁹⁾ and anti-proliferation activity against cancer cells.¹⁰⁾

Chart 1. Structures of Representative Endogenous N-Acyldopamines

NADA biosynthesis is considered to occur through direct conjugation of arachidonic acid with dopamine,¹¹⁾ which suggests that other endogenous N-acyldopamine species may exist for a number of fatty acids. However, the range of commercially-available N-acyldopamine species is limited. Here, we report a simple and efficient theoretically-applicable method for the synthesis of potentially all endogenous N-acyldopamines without the use of protective groups (Chart 2).

Chart 2. N-Acyldopamine Synthesis

We investigated the reaction conditions for direct amide bond formation between dopamine and fatty acid without any protective group, and we chose N-oleoyldopamine synthesis to establish a standard protocol consisting of: 1) condensation agents, 2) amines, 3) solvents, and 4) addition order of the reagents to the reaction flask (Chart 3).

Chart 3. N-Acyldopamine Synthetic Procedures Tested

1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI)¹²⁾ as the condensation agent always afforded O-acylated products 3 and 4 with low yields of the target amide 2 regardless of any combination of amine, solvent, or procedures 1–3 (Table 1, entries 1, 2, 5–9). Benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate (BOP)¹³⁾ showed the same efficacy as EDCI (entry 4). However, propylphosphoric anhydride (propylphosphoric acid cyclic anhydride, PPACA)⁴⁾ gave 2 exclusively (entry 3); therefore, this condensation agent was tested for further investigation using procedures 1 and 3 (entries 10–17). The best condition for the selective N-oleoyldopamine (2) synthesis is shown in entry 13, i.e., dopamine·HCl 1 eq, PPACA 1 eq, Et₃N 3 eq, in CH₂Cl₂ solvent with procedure 3 (Table 1). Although several N-acyldopamine syntheses were previously reported, for example, the mixed anhydride method,^1,10,14,15) EDCI method,¹²⁾ BOP method,¹³⁾ and O-(benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium tetrafluoroborate (TBTU) method,⁷⁾ PPACA was used by Walker’s group in 2003 for the synthesis of N-acyldopamine.⁴⁾ The advantages of PPACA as a condensation agent are that 1) PPACA shows a mild reactivity; therefore, byproducts 3 and 4 were not produced using this reagent, 2) PPACA is commercially available in solution; therefore, slow addition to a reaction flask was possible using a syringe in an Argon atmosphere. However, even PPACA produced byproducts 3 and 4 when this reagent was rapidly added to the reaction mixture.

Table 1. Conditions of Condensation Reaction and Products

Entry	Dopamine·HCl	Condensation agent	Amine	Solvent	Procedure	Product (yield (%))
1	1 eq	EDCI (1 eq)	DMAP (1 eq)	CH2Cl2	1	2 (0%)+3 (5.4%)+4 (31.2%)
2	1 eq	EDCI (1 eq)	DMAP (1 eq)	CH2Cl2	2	2 (0%)+3 (minor)+4 (major)
3	1 eq	PPACA (1 eq)	Et3N (3 eq)	CH2Cl2	2	2 (31.4%) (trace of 3 and 4)
4	1 eq	BOP (1 eq)	Et3N (3 eq)	CH2Cl2	2	2 (33.4%)+3 (trace)+4 (20.6%)
5	1 eq	EDCI (1 eq)	Et3N (3 eq)	CH2Cl2	2	2 (4.4%)+3 (trace)+4 (8.2%)
6	1 eq	EDCI (1 eq)	Et3N (3 eq)	CH2Cl2	1	2 (32.8%)+3 (trace)+4 (28.5%)
7	1 eq	EDCI (1 eq)	Et3N (3 eq)	CH2Cl2	3	2 (23.4%)+3 (trace)+4 (18.1%)
8	1 eq	EDCI (1 eq)	Et3N (3 eq)	DMF	1	2 (20.6%) (trace of 3 and 4)
9	1 eq	EDCI (1 eq)	Et3N (1 eq)	THF	1	2 (35.6%) (trace of 3 and 4)
10	1 eq	PPACA (1 eq)	Et3N (1 eq+2 eq)	CH2Cl2	1	2 (19.3%)
11	1 eq	PPACA (1 eq)	Et3N (2 eq)	CH2Cl2	1	2 (30.4%)
12	1 eq	PPACA (1 eq)	Et3N (3 eq)	CH2Cl2	1	2 (51.8%)
13	1 eq	PPACA (1 eq)	Et3N (3 eq)	CH2Cl2	3	2 (64.6%)
14	3 eq	PPACA (1 eq)	Et3N (3 eq)	CH2Cl2	1	2 (36.5%)
15	3 eq	PPACA (3 eq)	Et3N (3 eq)	CH2Cl2	1	2 (0%)+3 (minor)+4 (major)
16	3 eq	PPACA (1 eq)	Et3N (12 eq)	CH2Cl2	1	2 (trace)+3 (minor)+4 (major)
17	3 eq	PPACA (3 eq)	Et3N (12 eq)	CH2Cl2	1	2 (21.7%)

Utilizing the best reaction conditions described above, twenty N-acyldopamines, including the two deuterated analogs N-palmitoyl dopamine-d₅ and N-stearoyl dopamine-d₅ for internal standard use, were synthesized in total (Chart 4). The yields were moderate, and the starting materials could be recovered after silica-gel column chromatography. However, the use of excess reagents gave over-acylated products 3 and 4 (entries 15, 16, Table 1). This method was applicable to small-scale synthesis of the deuterated analogs¹⁶⁾ as well as using rare fatty acids. The reaction mixture in CH₂Cl₂ could be directly charged on silica-gel column chromatography as the purification step to yield pure N-acyldopamine in the small-scale synthesis.

Chart 4. Structures of Endogenous and Potentially Endogenous N-Acyldopamines Synthesized Including Deuterated Compounds with Reaction Yields

O-Acetylated analogs di-O-Ac-ODA and di-O-Ac-PALDA were obtained from diacetylation of ODA and PALDA, respectively.

Most of these analogs increased hypoxia inducible factor-1α expression, like the known endogenous N-acyldopamines.⁸⁾

Conclusion

The eighteen potentially endogenous N-acyldopamines and two deuterated ones, N-palmitoyl dopamine-d₅ and N-stearoyl dopamine-d₅, were efficiently synthesized without protective groups in CH₂Cl₂ under optimized conditions using PPACA as the condensation agent. The reaction mixture could be directly charged on silica-gel column chromatography as the purification step in small-scale synthesis. This method was also applicable for synthesizing deuterated N-acyldopamine analogs that can serve as internal standards for quantitative analysis. Thus, our simple and efficient synthetic method for N-acyldopamine synthesis may be useful for not only clarifying various functions and mechanisms of action of N-acyldopamines containing a specific fatty acid, but also for quantitating endogenous N-acyldopamines from biological samples.

Experimental

Representative Synthetic Procedure: N-Palmitoleoyl Dopamine

Dopamine hydrochloride (60.7 mg, 0.32 mmol) and palmitoleic acid (91.0 µL, 0.32 mmol) were mixed in dry CH₂Cl₂ (1 mL) under an Ar atmosphere, and triethylamine (133 µL, 0.96 mmol) was added at 0°C. PPACA (50% in ethyl acetate, 200 µL, 0.32 mmol) was slowly added over 30 min at the same temperature, and the reaction mixture was stirred at room temperature overnight. The mixture was worked up followed by evaporation, and the residue was purified by column chromatography (eluent; EtOAc–hexane=1 : 1–4 : 1) to give N-palmitoleoyl dopamine (22.6 mg, 18.1%) as a colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.86 (3H, t, J=6.9 Hz), 1.25–1.30 (16H, m), 1.56 (2H, m), 1.99 (4H, m), 2.14 (2H, t, J=7.8 Hz), 2.67 (2H, t, J=7.8 Hz), 3.46 (2H, q, J=6.7 Hz), 5.33 (2H, m), 5.70 (1H, t, J=5.6 Hz), 6.40 (1H, br s), 6.54 (1H, dd, J=2.0, 8.0 Hz), 6.73 (1H, d, J=2.0 Hz), 6.79 (1H, d, J=8.0 Hz), 7.91 (1H, br s). ¹³C-NMR (100 MHz, CDCl₃) δ: 14.2, 22.7, 25.8, 27.3, 27.3, 29.1–29.8 (multiple peaks in the range), 31.9, 35.0, 36.9, 41.1, 115.2, 115.5, 120.5, 129.8, 130.1, 130.4, 143.3, 144.5, 174.6. High resolution (HR)-MS Calcd for [C₂₄H₃₉NO₃+Na]⁺ ([M+Na]⁺) 412.2822. Found 412.2850.

N-Palmitoyl Dopamine-d₅

According to the same procedure as above using dopamine-d₅ hydrochloride (Cambridge Isotope Lab., Inc., 62.3 mg, 0.32 mmol) and palmitic acid (82.1 mg, 0.32 mmol), 48.9 mg of the product was obtained (38.5%) as a white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.23 (24H, m), 1.58 (2H, m), 2.11 (2H, t, J=7.8 Hz), 3.46 (2H, d, J=5.6 Hz), 5.36 (1H, br s), 5.45 (1H, br s), 6.36 (1H, br s). HR-MS Calcd for [C₂₄H₃₆D₅NO₃−H]⁻ ([M−H]⁻) 395.3328. Found 395.3327.

Physicochemical Data for the Synthetic N-Acyldopamine

N-Tridecanoyl Dopamine¹⁴⁾

A white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.86 (3H, t, J=6.9 Hz), 1.23–1.28 (18H, m), 1.57 (2H, m), 2.13 (2H, t, J=7.8 Hz), 2.69 (2H, t, J=7.1 Hz), 3.48 (2H, dt, J=7.1, 5.9 Hz), 5.55 (1H, br s), 5.74 (1H, br s), 6.57 (1H, dd, J=2.3, 8.2 Hz), 6.73 (1H, d, J=2.3 Hz), 6.79 (1H, d, J=8.2 Hz), 7.32 (1H, br s). ¹³C-NMR (100 MHz, CDCl₃) δ: 14.2, 22.8, 25.8, 29.3–29.7 (multiple peaks in the range), 32.0, 35.1, 37.0, 40.9, 115.2, 115.5, 120.6, 130.9, 143.0, 144.2, 174.6. HR-MS Calcd for [C₂₁H₃₅NO₃+Na]⁺ ([M+Na]⁺) 372.2509. Found 372.2494.

N-Myristoyl Dopamine¹⁴⁾

A white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.8 Hz), 1.23–1.29 (20H, m), 1.57 (2H, m), 2.13 (2H, t, J=7.6 Hz), 2.69 (2H, t, J=7.1 Hz), 3.48 (2H, dt, J=6.9, 6.4 Hz), 5.57 (1H, br s), 5.80 (1H, br s), 6.56 (1H, dd, J=2.3, 8.2 Hz), 6.73 (1H, d, J=2.3 Hz), 6.79 (1H, d, J=8.2 Hz), 7.40 (1H, br s). HR-MS Calcd for [C₂₂H₃₇NO₃+Na]⁺ ([M+Na]⁺) 386.2666. Found 386.2679.

N-Pentadecanoyl Dopamine¹⁴⁾

A white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.23–1.29 (22H, m), 1.58 (2H, m), 2.14 (2H, t, J=7.6 Hz), 2.69 (2H, t, J=7.1 Hz), 3.47 (2H, dt, J=7.1, 6.0 Hz), 5.57 (1H, br s), 5.84 (1H, br s), 6.56 (1H, dd, J=1.8, 7.8 Hz), 6.73 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=7.8 Hz), 7.51 (1H, br s). ¹³C-NMR (100 MHz, CDCl₃) δ: 14.2, 22.8, 25.8, 29.3–29.8 (multiple peaks in the range), 32.0, 34.9, 36.9, 40.5, 115.0, 115.2, 120.5, 129.8, 130.6, 143.1, 144.4, 174.1. HR-MS Calcd for [C₂₃H₃₉NO₃+Na]⁺ ([M+Na]⁺) 400.2822. Found 400.2843.

N-Palmitoyl Dopamine¹⁴⁾

A white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.23–1.29 (24H, m), 1.54 (2H, m), 2.11 (2H, t, J=7.6 Hz), 2.69 (2H, t, J=6.9 Hz), 3.47 (2H, dt, J=6.9, 6.4 Hz), 5.38 (1H, br s), 5.46 (1H, br s), 6.40 (1H, br s), 6.56 (1H, dd, J=2.3, 8.2 Hz), 6.73 (1H, d, J=2.3 Hz), 6.79 (1H, d, J=8.2 Hz). HR-MS Calcd for [C₂₄H₄₁NO₃+Na]⁺ ([M+Na]⁺) 414.2979. Found 414.2971.

N-Heptadecanoyl Dopamine¹⁴⁾

A white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.23–1.29 (26H, m), 1.55 (2H, m), 2.11 (2H, t, J=7.6 Hz), 2.69 (2H, t, J=6.9 Hz), 3.47 (2H, dt, J=6.9, 6.0 Hz), 5.40 (1H, br s), 5.46 (1H, br s), 6.46 (1H, br s), 6.58 (1H, dd, J=1.8, 8.2 Hz), 6.73 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=8.2 Hz). HR-MS Calcd for [C₂₅H₄₃NO₃+Na]⁺ ([M+Na]⁺) 428.3135. Found 428.3156.

N-Stearoyl Dopamine¹⁴⁾

A white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.23–1.29 (28H, m), 1.55 (2H, m), 2.11 (2H, t, J=7.6 Hz), 2.69 (2H, t, J=6.9 Hz), 3.47 (2H, dt, J=6.9, 6.0 Hz), 5.35 (1H, br s), 5.45 (1H, br s), 6.32 (1H, br s), 6.58 (1H, dd, J=1.8, 7.8 Hz), 6.73 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=7.8 Hz). HR-MS Calcd for [C₂₆H₄₅NO₃+Na]⁺ ([M+Na]⁺) 442.3292. Found 442.3294.

N-Nonadecanoyl Dopamine¹⁴⁾

A white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.23–1.29 (30H, m), 1.55 (2H, m), 2.10 (2H, t, J=7.6 Hz), 2.69 (2H, t, J=6.9 Hz), 3.47 (2H, dt, J=6.9, 6.4 Hz), 5.17 (1H, br s), 5.40 (1H, br s), 5.77 (1H, br s), 6.58 (1H, dd, J=1.8, 7.8 Hz), 6.73 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=7.8 Hz). HR-MS Calcd for [C₂₇H₄₇NO₃+Na]⁺ ([M+Na]⁺) 456.3448. Found 456.3468.

N-Eicosanoyl Dopamine¹⁴⁾

A white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.85 (3H, t, J=6.9 Hz), 1.22–1.26 (32H, m), 1.52 (2H, m), 2.07 (2H, t, J=7.8 Hz), 2.66 (2H, t, J=6.9 Hz), 3.43 (2H, t, J=6.9 Hz), 5.41 (1H, br s), 5.88 (1H, br s), 6.52 (1H, dd, J=1.8, 7.8 Hz), 6.67 (1H, d, J=1.8 Hz), 6.74 (1H, d, J=7.8 Hz). HR-MS Calcd for [C₂₈H₄₉NO₃+Na]⁺ ([M+Na]⁺) 470.3605. Found 470.3603.

N-Myristoleoyl Dopamine

A colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.25–1.32 (12H, m), 1.57 (2H, m), 1.96–2.03 (4H, m), 2.14 (2H, t, J=7.6 Hz), 2.68 (2H, t, J=7.1 Hz), 3.47 (2H, dt, J=7.1, 5.9 Hz), 5.31–5.34 (2H, m), 5.63 (1H, br s), 6.09 (1H, br s), 6.55 (1H, dd, J=1.8, 7.8 Hz), 6.73 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=7.8 Hz), 7.77 (1H, br s). HR-MS Calcd for [C₂₂H₃₅NO₃+Na]⁺ ([M+Na]⁺) 384.2509. Found 384.2520.

N-Sapienoyl Dopamine

A colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.86 (3H, t, J=6.9 Hz), 1.24–1.33 (16H, m), 1.58 (2H, m), 1.94–2.02 (4H, m), 2.16 (2H, t, J=7.6 Hz), 2.66 (2H, t, J=7.1 Hz), 3.45 (2H, dt, J=7.1, 5.9 Hz), 5.25–5.37 (2H, m), 5.89 (1H, br s), 6.52 (1H, dd, J=1.8, 7.8 Hz), 6.74 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=7.8 Hz). HR-MS Calcd for [C₂₄H₃₉NO₃+Na]⁺ ([M+Na]⁺) 412.2822. Found 412.2839.

N-(E)-Hexadec-9-enoyl Dopamine

A colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.86 (3H, t, J=6.9 Hz), 1.24–1.31 (16H, m), 1.56 (2H, m), 1.91–1.97 (4H, m), 2.14 (2H, t, J=7.6 Hz), 2.66 (2H, t, J=7.1 Hz), 3.48 (2H, dt, J=7.1, 5.9 Hz), 5.36 (2H, m), 5.74 (1H, br s), 6.53 (1H, dd, J=1.8, 7.8 Hz), 6.73 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=7.8 Hz), 7.91 (1H, br s). HR-MS Calcd for [C₂₄H₃₉NO₃+Na]⁺ ([M+Na]⁺) 412.2822. Found 412.2834.

N-(Z)-Hexadec-11-enoyl Dopamine

A colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.88 (3H, t, J=6.9 Hz), 1.23–1.33 (16H, m), 1.56 (2H, m), 1.97–2.01 (4H, m), 2.14 (2H, t, J=7.6 Hz), 2.68 (2H, t, J=7.1 Hz), 3.46 (2H, dt, J=7.1, 5.9 Hz), 5.32–5.35 (2H, m), 5.67 (1H, br s), 6.30 (1H, br s), 6.54 (1H, dd, J=1.8, 7.8 Hz), 6.73 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=7.8 Hz), 7.81 (1H, br s). HR-MS Calcd for [C₂₄H₃₉NO₃+Na]⁺ ([M+Na]⁺) 412.2822. Found 412.2827.

N-Petroselinoyl Dopamine

A colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.24–1.34 (20H, m), 1.58 (2H, m), 1.94–2.01 (4H, m), 2.15 (2H, t, J=7.6 Hz), 2.65 (2H, t, J=7.1 Hz), 3.44 (2H, dt, J=7.1, 5.9 Hz), 5.24–5.33 (2H, m), 5.89 (1H, br s), 6.52 (1H, dd, J=1.8, 7.8 Hz), 6.73 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=7.8 Hz). HR-MS Calcd for [C₂₆H₄₃NO₃+Na]⁺ ([M+Na]⁺) 440.3135. Found 440.3157.

N-Elaidoyl Dopamine¹⁷⁾

A colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.25–1.30 (20H, m), 1.58 (2H, m), 1.94 (4H, m), 2.13 (2H, t, J=7.6 Hz), 2.69 (2H, t, J=7.1 Hz), 3.47 (2H, dt, J=7.1, 5.9 Hz), 5.36 (2H, m), 5.54 (1H, br s), 5.74 (1H, br s), 6.56 (1H, dd, J=1.8, 7.8 Hz), 6.73 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=7.8 Hz). HR-MS Calcd for [C₂₆H₄₃NO₃+Na]⁺ ([M+Na]⁺) 440.3135. Found 440.3141.

N-cis-Vaccenoyl Dopamine

A colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.88 (3H, t, J=6.9 Hz), 1.23–1.28 (20H, m), 1.56 (2H, m), 1.99 (4H, m), 2.15 (2H, t, J=7.6 Hz), 2.65 (2H, t, J=7.1 Hz), 3.44 (2H, dt, J=7.1, 5.9 Hz), 5.33 (2H, m), 5.80 (1H, br s), 6.52 (1H, dd, J=1.8, 7.8 Hz), 6.72 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=7.8 Hz), 7.91 (1H, br s). HR-MS Calcd for [C₂₆H₄₃NO₃+Na]⁺ ([M+Na]⁺) 440.3135. Found 440.3143.

N-Linoleoyl Dopamine⁷⁾

A colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.24–1.36 (14H, m), 1.56 (2H, m), 1.99–2.06 (4H, m), 2.14 (2H, t, J=7.6 Hz), 2.64 (2H, t, J=7.1 Hz), 2.75 (2H, t, J=6.4 Hz), 3.43 (2H, dt, J=7.1, 5.9 Hz), 5.28–5.38 (4H, m), 5.88 (1H, t, J=5.7 Hz), 6.52 (1H, dd, J=1.8, 8.2 Hz), 6.73 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=8.2 Hz), 7.00 (1H, br s), 7.87 (1H, br s). ¹³C-NMR (100 MHz, CDCl₃) δ: 14.2, 22.7, 25.7, 25.9, 27.3, 29.2–29.8 (multiple peaks in the range), 31.6, 34.9, 36.9, 41.2, 120.5, 128.0, 128.2, 130.1, 130.3, 130.5, 143.3, 144.6, 174.8. HR-MS Calcd for [C₂₆H₄₁NO₃+Na]⁺ ([M+Na]⁺) 438.2979. Found 438.3003.

N-Eicosapentaenoyl Dopamine²⁾

A colorless oil. ¹H-NMR (400 MHz, CDCl₃) δ: 0.96 (3H, t, J=7.3 Hz), 1.67 (2H, m), 2.06 (4H, m), 2.15 (2H, t, J=7.6 Hz), 2.67 (2H, t, J=7.1 Hz), 2.75–2.82 (8H, m), 3.46 (2H, dt, J=7.1, 5.9 Hz), 5.28–5.40 (10H, m), 5.66 (1H, br s), 6.27 (1H, br s), 6.54 (1H, dd, J=1.8, 8.2 Hz), 6.73 (1H, d, J=1.8 Hz), 6.79 (1H, d, J=8.2 Hz), 7.75 (1H, br s). HR-MS Calcd for [C₂₈H₃₉NO₃+Na]⁺ ([M+Na]⁺) 460.2822. Found 460.2827.

N-Stearoyl Dopamine-d₅

A white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.87 (3H, t, J=6.9 Hz), 1.21–1.27 (28H, m), 1.56 (2H, m), 2.15 (2H, m), 3.50 (2H, m), 6.30 (1H, br s). HR-MS Calcd for [C₂₆H₃₉D₅NO₃−H]⁻ ([M−H]⁻) 423.3641. Found 423.3628.

Di-O-Ac-ODA

A white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.86 (3H, t, J=6.9 Hz), 1.23–1.29 (20H, m), 1.57 (2H, m), 1.99 (4H, m), 2.10 (2H, t, J=7.6 Hz), 2.26 (6H, s), 2.78 (2H, t, J=6.6 Hz), 3.47 (2H, dt, J=6.6, 5.2 Hz), 5.32 (2H, m), 5.55 (1H, br s), 6.99 (1H, d, J=1.8 Hz), 7.04 (1H, dd, J=1.8, 8.2 Hz), 7.10 (1H, d, J=8.2 Hz). HR-MS Calcd for [C₃₀H₄₇NO₅+K]⁺ ([M+K]⁺) 540.3086. Found 540.3085.

Di-O-Ac-PALDA

A white wax. ¹H-NMR (400 MHz, CDCl₃) δ: 0.86 (3H, t, J=6.9 Hz), 1.23–1.27 (24H, m), 1.57 (2H, m), 2.12 (2H, t, J=7.6 Hz), 2.26 (6H, s), 2.78 (2H, t, J=6.6 Hz), 3.47 (2H, dt, J=6.6, 6.0 Hz), 5.66 (1H, br s), 6.99 (1H, d, J=1.4 Hz), 7.04 (1H, dd, J=1.4, 8.2 Hz), 7.10 (1H, d, J=8.2 Hz). HR-MS Calcd for [C₂₈H₄₅NO₅+Na]⁺ ([M+Na]⁺) 498.3190. Found 498.3207.

Acknowledgments

We thank Mr. Elliot Bradshaw (RIKEN) for proofreading. This work was supported in part by Grants-in-Aid from the Japan Society for the Promotion of Science (No. 24790004 to Y.M. and No. 24590021 to A.K.) and AMED-CREST, AMED.

Conflict of Interest

The authors declare no conflict of interest.

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