Structural and stereochemical aspects of base-catalyzed double bond isomerization of sterols with unsaturated side chains

Abstract

A careful analysis of the N-lithioethylenediamine-catalyzed isomerization of 22-, 23-, and 24-methylenecholesterol demonstrated the existence of subtle factors which are responsible for the kinetically and thermodynamically preferred products. In general, the results can be related to the anticipated energy preferences of the intermediate carbanions. Through the use of 'H and 13C NMR spectroscopy the configuration of the various double bond isomers could be established. Since all major products are readily separated by HPLC, such base-catalyzed isomerization offers a convenient synthetic route to a variety of stereochemically pure sterol olefins, which either have been found in the marine environment or may be detected in the future.

A New Polyhydroxy Sterol from the Soft CoralLobophytumcrassum,1

“…The respective monohydroxylated and polyhydroxylated sterol mixtures were acetylated and were separated on 20% AgNO 3 -impregnated Si gel column. The 5% CH 3 COCH 3 in hexane fraction afforded (22 R ,23 R )-methylene cholesterol (500 mg), ergost-5,22-dien-3β-ol (30 mg), ergost-5,25-dien-3β-ol (20 mg), and 24-methylenecholesterol (20 mg) . The 25% CH 3 COCH 3 in hexane fraction yielded (24 S )-ergostane-3β,5α,6β,25-tetrol 25-monoacetate (500 mg) …”

“…The sterol mixture fractions were acetylated using Ac 2 O and pyridine and then separated by chromatography on a Silica gel column impregnated with silver nitrate. A total of eight known sterols, (22R,23R)-methylenecholesterol, 9 ergost-5,22-diene 3β-ol, 10 ergost-5,25-dien-3βol, 11 24-methylenecholesterol, 12 (24S)-ergostane-3β,5R,6β,-25-tetrol 25-monoacetate, 13 (24S)-ergostane-3β,5R,6β,25tetrol, 13 (24S)-ergostane-1β,3β,5R,6β-tetrol-1,3,6-triacetate, 14,15 24-methylene cholestane-1β,3β,5R,6β-tetrol, 15 and a new polyhydroxy sterol (1) were isolated.…”

Steroids: reactions and partial syntheses

“…~~ The (n-ally1)palladium complexes (44) and (45) were reduced to isotachysterol, and ergosta-4,6,8( 14),22-tetraene respectively, and oxidation of (45) with MCPBA gave the 3a-hydroxy-tetraene (46). Reactions of aand P-l-3q-type (n-ally1)palladium complexes with KOAc gave 3-acetoxycholest-1 -ene derivatives having the trans configuration with respect to the original co-ordinated palladium, while reactions of A'and A2-cholestenes with PdC1, and CuCl, and AcOK in acetic acid afforded the 1 a-acetoxy-derivatives arising from cis-atta~k.~ Alkylation of the (n-ally1)palladium complex of testosterone with the anion of methyl phenylsulphonylacetate affordeds2 the 6P-derivative (47).…”

Constituents of the Leaves of Pandanus Utilis

“…2b). Referring to literature [10,11], lanostanoids biosynthesize along the same pathway, and maintain the same geometry. The junction proton H-5 was assigned an α-orientation, while Me-19 had a β-direction, as usual.…”

“…(n = 3). * P < 0.05, ** P < 0.01, and *** P < 0.001 were compared with the control value.The other isolates were identified as (24S)-24-methyl-25,32-cyclocycloartane-3-ol (2)[12], 24-methyl-25,32-cyclo-5-lanosta-9(11)-en-3-ol (3)[12], 24,24-dimethyl-5-lanosta-9(11),25-dien-3-ol (4) [10], (24R)-24-methyl-5-lanosta-9(11),25-dien-3-ol(5) [10], (24S)-24-methyl-5-lanosta-9(11),25-dien-3-ol(6) [10], and lanost-9(11)-en-3-ol(7) [10], cholesterol (8)[13], -sitosterol (9)[14], stigmasterol (10)[14], -sitosterone(11) [15], stigmasta-4,22dien-3-one(12) [15], vomifoliol (13)[16], (S)-dehydrovomifoliol(14) [17], byzantioside B (15)[18], (6R, 9R)-3 oxo--ionol -Dglucoside (16)[19], benzyl -D-glucoside (17)[20], 2-phenylethyl -D-glucoside (18)[20], and pinoresinol 4-O--D-glucopyranoside(19) [21]. Among them, cyclohexenone derivatives 1316 are reported for the first time from a Pandanus species.Anti-inflammatory, anti-oxidative, and cytotoxic activities of the ethyl acetate portion (PU-E), the aqueous portion (PU-H), and the isolates are shown in Tables 13, respectively.…”