Synthesis of hydroxy acids of dinorcholane and 5β-cholane

ARTICLE

Synthesis of hydroxy acids of dinorcholane and 5β-cholane

L. Nahar^*,I; A. B. Turner^II; S. D. Sarker^I

^IDepartment of Pharmacy, School of Applied Sciences, University of Wolverhampton, City Campus-South, Wulfruna Street, Wolverhampton WV1 1LY, England, UK

^IIJapp Laboratory, Department of Chemistry, University of Aberdeen, Aberdeen AB24 3UE, Scotland, UK

ABSTRACT

A diastereomeric mixture (55:45) of 3-oxo-23,24-dinorchol-4-en-22-hydroxy acids (4A and 4B) was synthesized from 3-oxo-23,24-dinorchol-4-en-22-al (1) in 3 steps. Similarly, 3-oxo-5β-cholane-24-hydroxy acid (9) was synthesized from 5β-cholane-3α,24-diol (5) in 4 steps. Full spectroscopic data for these compounds are presented.

Keywords: 3-oxo-23,24-dinorchol-4-en-22-al, 3-oxo-5β-cholane-24-al, cyanohydrin silyl ether, hydroxy acid, NMR

RESUMO

Uma mistura diastereomérica (55:45) de 3-oxo-23,24-dinorcol-4-en-22-hydroxi ácidos (4A e 4B) foi sintetizada a partir de 3-oxo-23,24-dinorcol-4-en-22-al (1) em 3 etapas. Similarmente, 3-oxo-5β-cholano-24-hidroxi ácido (9) foi sintetizado a partir de 5β-cholano-3α,24-diol (5) em 4 etapas. Dados espectroscópicos completos para estes compostos são apresentados.

Introduction

Enantiopure α-hydroxy acids (AHAs) are versatile building blocks in organic synthesis. They are used for obtaining pharmaceutically and biologically active substances, such as vitamins. α-Hydroxy acids are easily synthesized from cyanohydrins. Thus, molecules with cyanohydrin substructures are interesting intermediates for the synthesis of AHAs.¹ Usually, cyanohydrins are prepared by the addition of a cyanide group to the carbonyl carbon of aldehydes or ketones resulting in enantiomeric mixtures of optically active cyanohydrins when aldehydes or asymmetric ketones are employed. However, if a chiral centre already exists next to the carbonyl carbon, two possible diastereomeric products are formed, and they are not of equal amounts. As part of our on-going studies on the synthesis and reactions of steroid monomers and dimers,^2-8 we now report on the development of a convenient and general method for the synthesis of diasteriomerc (55:45) dinorcholane hydroxy acids and 5β-cholane hydroxy acid using readily available dinorcholanal and 5β-cholane-3α,24-diol as the starting materials.

Results and Discussion

The cyanation reaction of carbonyl compounds is one of the most powerful procedures for the synthesis of cyanohydrins or cyanohydrin trimethylsilyl ethers. These products can easily be converted to a variety of other acid derivatives, such as α-hydroxy carboxylic acids, α-hydroxy aldehydes, β-amino alcohols and α-amino acids.¹ Several useful cyanating reagents are available, but among them, trimethylsilyl cyanide (TMSCN) is one of the most effective and safe cyanating sources for nucleophilic addition to carbonyl compounds.⁹

When an achiral nucleophile adds to an achiral aldehyde, a chiral centre is formed, which is a racemic mixture. However, when a chiral centre is present next to the carbonyl carbon, two possible diastereomeric products are formed. Thus, the reaction of 3-oxo-23,24-dinorchol-4-en-22-al (1) with TMSCN produced a diastereomeric mixture (55:45) of 22-cyanohydrin silyl ethers (2A and 2B) (Scheme 1).

The FABMS spectrum of the mixture revealed the [M+H]⁺ and [M+Na]⁺ ions, respectively, at m/z 428 and 450. The presence of a CΞN moiety was evident from the IR absorption band at 2229 cm^-1. Among the ¹H NMR signals, the two most important peaks were at d 0.17 (s, 9H, 3 × Me), 4.42 and 4.38 (bd, 1H), which confirmed the presence of a TMS unit at C-22. In the ¹³C NMR spectrum of this mixture, apart from the signals confirming the above findings, the most revealing signals were a pair of signals at d 64.8 and 65.0 for the oxymethine (C-22, 2A and 2B) and another pair of signals at d 120.1 and 118.3 for the CΞN carbon of two diastereomeric isomers 2A and 2B. The diastereomeric ratio was determined by ¹³C NMR spectroscopic integration.

The diastereomeric 22-cyanohydrin silyl ethers (2A and 2B) were refluxed 18 h using NH₃ (25%) in THF and the reaction mixture was washed with dil. HCl to obtain the 22-cyanohydrin. The products obtained were found to be a diastereomeric mixture of 22-cyanohydrins 3A and 3B (Scheme 1). A portion of the mixture was subjected to preparative reversed-phase HPLC resulting in the isolation of pure 3A and 3B. The isomer 3A was eluted first with the retention time of 17.1 min, followed by the isomer 3B having the retention time of 18.3 min. The diastereomeric ratio (55:45) was obtained from the HPLC signals. The compound 3A and 3B had different melting points, and they were 230 ºC and 189-190 ºC, respectively.

In the ¹H NMR of 3A, the most important peak was a doublet at d 4.53 (J 4.1 Hz) for the oxymethine at C-22, indicating the presence of a cyanohydrin unit at C-22. The ¹³C NMR showed characteristic signals for the carbons, C-22 and CΞN at d 64.9 and 122.4, respectively.³ The ¹H NMR of 3B was similar to that of 3A with the exception that the resonance for the C-22 oxymethine (d 4.48, J 4.1 Hz) was slightly less deshielded than 3A. The ¹³C NMR of 3B was also similar to that of 3A with the exception that the characteristic signals for the carbons, C-22 and CΞN were observed at d 65.2 and 118.4, respectively. Unambiguous assignment of all ¹H and ¹³C resonances were achieved by ¹H-¹³C HSQC and ¹H-¹³C HMBC experiments. The [M+H]⁺ and [M+Na]⁺ ions of both isomers were observed, respectively, at m/z 356 and 378 in their FABMS spectra. The presence of OH and CΞN functionalities, in both cases, was supported from the IR absorption bands at 3336 and 2235 cm^-1, respectively.

Acid hydrolysis of the diastereomeric mixture 3A and 3B in MeOH yielded the diastereomeric mixture of 22-hydroxy acids 4A and 4B (Scheme 1). The IR spectrum of this mixture showed the absorption bands characteristic for acid and alcohol hydroxyls at 3453 (acidic O-H), 3383 (alcoholic O-H), and acid carbonyl at 1720 cm^-1. In the ¹H NMR spectrum, a broad doublet at d 3.68/3.63 for an oxymethine proton indicated the presence of a hydroxyl group at C-22 of diastereomeric isomers 4A and 4B. The ¹³C NMR spectrum of this mixture displayed a pair of signals at d 161.2/161.0 for the acid carbonyl carbon at C-22, and a pair of signals at d 64.9 and 65.2 for the oxymethine (C-22) of diastereomeric isomers 4A and 4B. The diastereomeric ratio was determined by ¹³C NMR spectroscopic integration. The FABMS spectrum revealed the [M+H]⁺ and [M+Na]⁺ ions, respectively, at m/z 375 and 397.

As outlined in Scheme 2, 3-oxo-5β-cholane-24-hydroxy acid (9) was synthesized from the diol 5 in 4 steps. In the first step, diol 5 was oxidized using PCC in DCM to obtain 5β-cholanal 6.¹⁰ The FABMS spectrum of 6 revealed the [M+H]⁺ and [M+Na]⁺ ions, respectively, at m/z 359 and 381. In its ¹³C NMR spectrum, the signals at d 213.4 and 203.1 established, respectively, the presence of 3-oxo and C-24 aldehyde functionalities.

3-Oxo-24-cyanohydrin silyl ether 7 was obtained from 6 in MeCN using TMSCN (Scheme 2). The FABMS spectrum of 7 revealed the [M+H]⁺ and [M+Na]⁺ ions at m/z 458 and 480, respectively. In its IR spectrum the absorption band at 2238 cm^-1 was indicative of a CΞN stretching. In the ¹H NMR spectrum the signals for the protons associated with C-1 to C-24 of 7 were almost similar to those of 6, except that a signal at d 4.31 for the oxymethine proton of C-24 (instead of an aldehyde proton at d 9.50 in 6) and a 9H singlet for the TMS group were present at d 0.19. The ¹³C NMR spectrum also corroborated this fact by showing signals at d 61.9, 120.2 and -0.4, respectively, for the C-24 oxymethine, nitrile and TMS carbons.

The 24-cyanohydrin silyl ether 7 was treated with NH₃ (25%) and refluxed for 18h then washed with dil. HCl to yield 24-cyanohydrin 8 (Scheme 2). The FABMS spectrum of 8 revealed the [M+H]⁺ and [M+Na]⁺ ions at m/z 386 and 408, respectively. In its IR spectrum the absorption bands at 3452 and 2241 cm^-1 were indicative of alcohol OH and CΞN stretchings. The ¹H and ¹³C NMR spectra of 8 were similar to those of 7 with the exception that there was no signal for a TMS group, and both C-24 oxymethine and nitrile signals were slightly deshielded.

Acid hydrolysis of the 24-cyanohydrin 8 in MeOH yielded 24-hydroxy acid 9 (Scheme 2). The IR spectrum showed the absorption bands characteristic for acid and alcohol hydroxyls, respectively, at 3458 and 3454 cm^-1, and an acid carbonyl at 1728 cm^-1. In the ¹H NMR spectrum of 9, a broad doublet at d 3.62 for an oxymethine proton indicated the presence of a hydroxyl group and an acid group at C-24. The ¹³C NMR spectrum displayed a signal at d 162.0 for the acid carbonyl carbon at C-24, and a signal at d 62.4 for the oxymethine (C-24). The FABMS spectrum revealed the [M+H]⁺ and [M+Na]⁺ ions, respectively, at m/z 405 and 427.

This study established facial synthetic routes for the synthesis of diastereomeric mixture (55:45) of 3-oxo-23,24-dinorchol-4-en-22-hydroxy acids (4A and 4B) from 3-oxo-23,24-dinorchol-4-en-22-al (1), and 3-oxo-5β-cholane-24-hydroxy acid (9) from 5β-cholane-3α,24-diol (5). On the basis of spectroscopic data obtained for compound 9, it was not possible to confirm if this compound was a pure enantiomer or a racemic mixture. However it was certain that this compound (9) could not be a diastereomeric mixture, because there was no stereo centre next to the carbonyl (reactive centre).

Experimental

General

The starting material 5β-cholane-3α,24-diol (5) was previously synthesized and identified in our lab.² 3-Oxo-23,24-dinorchol-4-en-22-al (1), pyridinium chlorochromate (PCC) and trimethylsilyl cyanide (TMSCN) were purchased from Aldrich and used as received. The reactions were monitored and the purity of the products was assessed by thin-layer chromatography (TLC) performed on silica gel (Merck type 60) and visualized under UV illumination and/or by I₂ vapor. Melting points of the products were determined on a Gallen-kamp melting point apparatus. Infrared spectra (wave numbers in cm^-1) were recorded on an ATI Mattson Genesis FTIR spectrophotometer either as KBr pellets or in CHCl₃. Nuclear magnetic resonance (NMR) spectra were recorded on a Varian Unity INOVA 400 MHz NMR spectrometer. NMR spectra were obtained in CDCl₃. Chemical shifts (d) are reported in ppm downfield from TMS, using the residual solvent peak (7.25 ppm for ¹H and 77.23 ppm for ¹³C) as an internal standard and coupling constants (J) in Hz. Mass spectroscopic analyses were performed at the EPSRC Mass Spectrometry Service at Swansea.

Synthesis of diastereomeric 3-oxo-23,24-dinorchol-4-ene-22-cyanohydrin silyl ether (2A and 2B)

To a stirred solution of 3-oxo-23,24-dinorchol-4-en-22-al (1, 200 mg, 0.61 mmol) in MeCN (8 mL), TMSCN (266 mg, 4.4 equiv.) was added under N₂ and the reaction was monitored by TLC. After 12 h the reaction mixture was evaporated to dryness to obtain a dark yellow oil, which was purified by Vacuum Liquid Chromatography (VLC) (30% EtOAc in pet-ether) to yield a white solid as a diastereomeric mixture (55:45) of the title compound 2A and 2B. Yield: 246 mg (94%), mp 140-141 ºC. IR (CHCl₃) ν_max/cm^-1: 2935 (C-H), 2852 (C-H), 2229 (CΞN), 1666 (ketonic C=O), 1616 (C=C), 1460, 1253 (ether C-O), 1186, 1105, 1040, 937, 879, 847, 752 and 654. ¹H NMR (400 MHz, CDCl₃): d 0.17 (s, 9H, OTMS), 0.69 (s, 3H, 18-Me), 1.10 (d, J 5.2 Hz, 3H, 21-Me), 1.15 (s, 3H, 19-Me), 4.42 (br d, 1H, 22-OCH, 2A) and 4.38 (br d, 1H, 22-OCH, 2B), 5.68 (s, 1H, 4-CH). ¹³C NMR (100 MHz, CDCl₃): d 35.4 (C-1), 33.6 (C-2), 199.2 (C-3), 123.5 (C-4), 171.0 (C-5), 32.5 (C-6), 31.6 (C-7), 35.3 (C-8), 51.1 (C-9), 38.2 (C-10), 20.7 (C-11), 39.0 (C-12), 42.3 (C-13), 53.3 (C-14), 24.0 (C-15), 27.2 (C-16), 55.1 (C-17), 11.8 (C-18), 17.1 (C-19), 42.0 (C-20), 13.4 (C-21), 64.8 (C-22, 2A) and 65.0 (C-22, 2B), 120.1 (C-23, 2A) and 118.3 (C-23, 2B), -0.3 (OTMS). FABMS m/z: 428 [M+H]⁺, 450 [M+Na]⁺. HR-FABMS m/z: [M+H]⁺ 428.2979; calc. 428.2979 for C₂₆H₄₂NO₂Si.

Synthesis of diastereomeric 3-oxo-23,24-dinorchol-4-ene-22-cyanohydrin (3A and 3B)

To a stirred solution of the mixture of 2A and 2B (225 mg, 0.53 mmol) in THF (8 mL), 25% NH₃ (5 mL) was added and the mixture was refluxed for 18 h. Dilute HCl was added to the reaction mixture, extracted with CHCl₃ and washed with H₂O to obtain 22-cyanohydrin (3). The solid was cleaned up by VLC (40% EtOAc in pet-ether) to yield as a diastereomeric mixture (55:45) of the title compound 3A and 3B. Yield: 155 mg (82%). Small portion of the mixture of 3A and 3B was separated by preparative reversed-phase HPLC using a LUNA C₁₈ preparative column (250 mm × 21.2 mm, 10 μm), eluted with a linear gradient: 45-100% acetonitrile in water in 40 minutes, followed by 100% acetonitrile for 10 min, flow rate = 20 mL min^-1, monitored by a photo-diode-array detector (Figure 1).

The purified 22-cyanohydrin 3A was obtained as crystals, mp 230 ºC; ¹H NMR (400 MHz, CDCl₃): d 4.53 (d, J 4.1 Hz, 1H, 22-OCH); ¹³C NMR (100 MHz, CDCl₃): d 64.9 (C-22), 122.4 (C-23) (lit. mp 230 ºC, IR, ¹H NMR, ¹³C NMR and FABMS).³

The purified 22-cyanohydrin 3B was obtained as a white amorphous solid, mp 189-190 ºC. IR (CHCl₃) ν_max/cm^-1: 3336 (O-H), 2945 (C-H), 2873 (C-H), 2235 (CΞN), 1670 (ketonic C=O), 1616 (C=C), 1448, 1379, 1254, 1072, 935, 847 and 756. ¹H NMR (400 MHz, CDCl₃): d 0.76 (s, 3H, 18-Me), 1.09 (d, J 6.5 Hz, 3H, 21-Me), 1.19 (s, 3H, 19-Me), 4.48 (d, J 4.1 Hz, 1H, 22-OCH), 5.67 (s, 1H, 4-CH). ¹³C NMR (100 MHz, CDCl₃): d 35.5 (C-1), 33.9 (C-2), 199.7 (C-3), 123.9 (C-4), 171.3 (C-5), 32.8 (C-6), 31.9 (C-7), 35.6 (C-8), 52.0 (C-9), 38.5 (C-10), 20.9 (C-11), 39.3 (C-12), 42.8 (C-13), 53.6 (C-14), 24.2 (C-15), 27.4 (C-16), 55.3 (C-17), 12.1 (C-18), 17.4 (C-19), 41.1 (C-20), 13.2 (C-21), 65.2 (C-22), 118.4 (C-23). FABMS m/z: 356 [M+H]⁺, 378 [M+Na]⁺. HR-FABMS m/z: [M+H]⁺ 356.2583; calc. 356.2584 for C₂₃H₃₄NO₂.

Synthesis of diastereomeric 3-oxo-23,24-dinorchol-4-ene-22-hydroxy acid (4A and 4B)

To a solution of 2 (100 mg, 0.28 mmol) in THF (8 mL), conc. HCl (2 mL) was added, and the mixture was stirred under reflux for 24h. Solvent was removed under reduced pressure. The residue was dissolved in DCM and saturated NaHCO₃ was added to neutralize the HCl, and the mixture was extracted with DCM, washed with H₂O and dried over MgSO₄. The solid was identified as a diastereomeric mixture (55:45) of the title compound 4A and 4B as slowly solidifying yellow oil. Yield: 56 mg (53%), mp 179-180 ºC. IR (CHCl₃) ν_max/cm^-1: 3453 (acidic O-H), 3383 (alcoholic O-H), 2938 (C-H), 2860 (C-H), 1720 (acidic C=O), 1674 (ketonic C=O), 1618 (C=C), 1464, 1378, 1269, 1223, 1188, 1060, 867 and 750. ¹H NMR (400 MHz, CDCl₃): d 0.73 (s, 3H, 18-Me) and 0.72 (s, 3H, 18-Me), 1.15 (d, J 6.7 Hz, 3H, 21-Me), 1.17 (s, 3H, 19-Me), 3.68 (br d, 1H, 22-OCH, 4A) and 3.63 (br d, 1H, 22-OCH, 4B), 5.72 (s, 1H, 4-CH). ¹³C NMR (100 MHz, CDCl₃): d 35.7 (C-1), 34.1 (C-2), 200.7 (C-3), 125.9 (C-4), 172.6 (C-5), 33.1 (C-6), 32.1 (C-7), 35.6 (C-8), 52.2 (C-9), 39.0 (C-10), 21.1 (C-11), 39.5 (C-12), 43.2 (C-13), 53.9 (C-14), 24.3 (C-15), 27.5 (C-16), 56.2 (C-17), 12.2 (C-18), 17.8 (C-19), 41.3 (C-20), 13.9 (C-21), 64.9 (C-22, 4A) and 65.2 (C-22, 4B), 161.2 (C-23, 4A) and 161.0 (C-23, 4B). FABMS m/z: 375 [M+H]⁺, 397 [M+Na]⁺. HR-FABMS m/z: [M+H]⁺ 375.25298; calc. 375.25299 for C₂₃H₃₅O₄.

Synthesis of 3-oxo-5β-cholan-24-al (6)

A solution of 5β-cholan-3α,24-diol (5, 370 mg, 1.03 mg) in dry DCM (40 mL) was treated with PCC (440 mg, 2 molar equiv.), and the mixture was refluxed for 18h under N₂. The reaction was quenched with H₂O and extracted with ether. The ethereal solution was washed with H₂O, NaHCO₃ and brine, dried over MgSO₄. The compound was purified by VLC (20% EtOAc in pet-ether) and identified as the title compound 6. Yield: 287 mg (78%), mp 81-82 ºC (lit. mp 82-83 ºC, IR and ¹H NMR).^{10 13}C NMR (100 MHz, CDCl₃): d 37.2 (C-1), 37.0 (C -2), 213.4 (C-3), 42.3 (C-4), 44.3 (C-5), 25.8 (C-6), 26.6 (C-7), 35.3 (C-8), 40.7 (C-9), 34.9 (C-10), 21.2 (C-11), 40.3 (C-12), 42.8 (C-13), 56.4 (C-14), 24.1 (C-15), 28.1 (C-16), 56.0 (C-17), 12.1 (C-18), 22.6 (C-19), 35.5 (C-20), 18.2 (C-21), 27.9 (C-22), 30.7 (C-23), 203.1 (C-24). FABMS m/z: 359 [M+H]⁺, 381 [M+Na]⁺.

Synthesis of 3-oxo-5β-cholane-24-cyanohydrin silyl ether (7)

A solution of 6 (200 mg, 0.56 mmol) in dry MeCN (8 mL) was treated with TMSCN (244 mg, 4.4 molar equiv.), and the mixture was refluxed for 12 h under N₂. After rotary evaporation, the crude solid was purified by Preparative Thin Layer Chromatography (PTLC) (30% EtOAc in pet-ether) and the title compound 7 was obtained as a yellowish thick gum. Yield: 160 mg (62%). IR (CHCl₃) ν_max/cm^-1: 2953 (C-H), 2856 (C-H), 2238 (CΞN), 1726 (ketonic C=O), 1460, 1379, 1277, 1120, 1076, 847 and 744. ¹H NMR (400 MHz, CDCl₃): d 0.19 (s, 9H, OTMS), 0.63 (s, 3H, 18-Me), 0.88 (d, J 6.5 Hz, 3H, 21-Me), 0.97 (s, 3H, 19-Me), 4.31 (br t, 1H, 24-CH-O). ¹³C NMR (100 MHz, CDCl₃): d 37.3 (C-1), 37.1 (C-2), 213.5 (C-3), 41.0 (C-4), 44.4 (C-5), 25.8 (C-6), 26.7 (C-7), 35.4 (C-8), 40.8 (C-9), 35.0 (C-10), 21.3 (C-11), 40.1 (C-12), 42.4 (C-13), 56.5 (C-14), 24.2 (C-15), 28.3 (C-16), 56.1 (C-17), 12.1 (C-18), 22.7 (C-19), 35.6 (C-20), 18.5 (C-21), 33.0 (C-22), 30.7 (C-23), 61.9 (C-24), 120.2 (C-25), -0.4 (24-OTMS). FABMS m/z: 458 [M+H]⁺, 480 [M+Na]⁺. HR-FABMS m/z: [M+H]⁺ 458.3448; calc. 458.3449 for C₂₈H₄₈NO₂Si.

Synthesis of 3-oxo-5β-cholane-24-cyanohydrin (8)

A solution of 7 (150 mg, 0.33 mmol) in dry THF (5 mL) was treated with 25% NH₃ (5 mL), and the mixture was refluxed for 18 h, extracted with CHCl₃ and washed with H₂O, dil. HCl and brine, dried over MgSO₄. The solvent was evaporated at reduced pressure to afford a crude solid which was purified by PTLC (40% EtOAc in pet-ether) and the title compound 8 was obtained as an oil. Yield: 81 mg (64%). IR (CHCl₃) ν_max/cm^-1: 3452 (O-H), 2939 (C-H), 2862 (C-H), 2241 (CΞN), 1726 (ketonic C=O), 1450, 1379, 1254, 1119, 1078, 866 and 755. ¹H NMR (400 MHz, CDCl₃): d 0.68 (s, 3H, 18-Me), 0.93 (d, J 6.5 Hz, 3H, 21-Me), 0.99 (s, 3H, 19-Me), 4.41 (br t, 1H, 24-OCH). ¹³C NMR (100 MHz, CDCl₃): d 37.3 (C-1), 37.1 (C -2), 213.5 (C-3), 41.0 (C-4), 44.3 (C-5), 25.8 (C-6), 26.7 (C-7), 35.2 (C-8), 42.3 (C-9), 35.2 (C-10), 21.5 (C-11), 40.1 (C-12), 42.4 (C-13), 56.6 (C-14), 24.3 (C-15), 28.2 (C-16), 56.2 (C-17), 12.3 (C-18), 22.9 (C-19), 35.7 (C-20), 18.8 (C-21), 33.2 (C-22), 30.9 (C-23), 30.9 (C-23), 62.3 (C-24), 122.0 (C-25). FABMS m/z: 386 [M+H]⁺, 408 [M+Na]⁺. HR-FABMS m/z: [M+H]⁺ 386.3053; calc. 386.3054 for C₂₅H₄₀NO₂.

Synthesis of 3-oxo-5β-cholane-24-hydroxy acid (9)

To a solution of 8 (75 mg, 0.19 mmol) in THF (5 mL), conc. HCl (2 mL) was added, and the mixture was stirred under reflux for 24h. The solvent was removed under reduced pressure. The residue was dissolved in DCM and saturated NaHCO₃ was added to neutralize the HCl, and the mixture was extracted with DCM, washed with H₂O, dried over MgSO₄. The solvent was evaporated at reduced pressure to afford a crude product which was purified by PTLC (40% EtOAc in pet-ether) and the title compound 9 was obtained as an oil. Yield: 53 mg (69%). IR (CHCl₃) ν_max/cm^-1: 3458 (acidic O-H), 3454 (alcoholic O-H), 2938 (C-H), 2863 (C-H), 1728 (ketonic C=O), 1452, 1378, 1255, 1118, 1079, 868 and 756. ¹H NMR (400 MHz, CDCl₃): d 0.68 (s, 3H, 18-Me), 0.92 (d, J 6.5 Hz, 3H, 21-Me), 0.98 (s, 3H, 19-Me), 3.62 (br d, 1H, 24-OCH). ¹³C NMR (100 MHz, CDCl₃): d 37.3 (C-1), 37.1 (C -2), 213.5 (C-3), 41.0 (C-4), 44.3 (C-5), 25.8 (C-6), 26.7 (C-7), 35.2 (C-8), 42.3 (C-9), 35.2 (C-10), 21.5 (C-11), 40.1 (C-12), 42.4 (C-13), 56.6 (C-14), 24.3 (C-15), 28.2 (C-16), 56.2 (C-17), 12.3 (C-18), 22.9 (C-19), 35.7 (C-20), 18.8 (C-21), 33.2 (C-22), 30.9 (C-23), 62.4 (C-24), 162.0 (C-25). FABMS m/z: 405 [M+H]⁺, 427 [M+Na]⁺. HR-FABMS m/z: [M+H]⁺ 405.2999; calc. 405.2999 for C₂₅H₄₁O₄.

Acknowledgments

The authors thank the funding body the development trust fund for a PhD studentship (L.N.) and EPSRC National Mass Spectrometry Service Centre (Department of Chemistry, University of Wales Swansea, Swansea, UK) for MS analysis.

Received: July 15, 2008

Web Release Date: November 14, 2008

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Publication Dates

• Publication in this collection
  15 Jan 2009
• Date of issue
  2009

History

• Received
  15 July 2008
• Accepted
  14 Nov 2008