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Minor and trace sterols in marine invertebrates 52. isolation, structure elucidation and partial synthesis of 24-propyl-24,28-methylenecholest-5-en-3β-ol

✍ Scribed by T.B. Tam Ha; Carl Djerassi

Publisher
Elsevier Science
Year
1985
Tongue
French
Weight
257 KB
Volume
26
Category
Article
ISSN
0040-4039

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✦ Synopsis

The isolation and structure elucidation of the first cyclopropyl-containing m(1) resulting from quadruple bioalQlation of the sterol side chain is reported.

Recently we reported' the discovery of several new sterols in a Pseudaxinissa species from the Australian Great Barrier Reef. This spo n@ e had been reported to contain only 24isopropylcholesterol and its 22-dehydro analog. We nowcommunicatethe discovery of a novel cyclopropane-containing sterol arising from quadruple biomethylation of the cholesterol sidechain.

Fractionation of the sponge sterol mixture (700mg)by reverse phaseHPLC provided, along with previously described component 7, several new sterols5 among which was a cyclopropyl sterol (readily identifpble by HNMR signals 60.5 -60.2). Repeated reverse phase HPLC (2x Altex Ultrasphere mobile phase MeOH or MeCN/BtOAc/MeOH 3/l/l) eventually gave the pure sterol 1. The molecular weight of 440 (C31H5 0) coupled with the mass spectral fragments at 271, 255, 229 and 213 typical6 of a conven ional z cholesterol nucleus indicated that all the extra carbons had to be in the side chain. A fragment ion of mass 397 (M-C.$I,) resulting from cleavage of the three membered ring (2) pointed to the presence of an ethyl-substituted cyclopropane. The 300 MHz lH NMR spectrum (Table 1) showed three one-proton resonances at low field indicative of a tri-substituted cyclopropyl ring system. Signals due to three secondary methyl groups (C21, C26 and C27), one ethyl group (CR) and the Cl8 and Cl9 methyl substituents were also apparent. Irradiation of the secondary methyl groups confirmed that none was attached to the cyclopropane ring. basic biosynthetic considerations7 (s,

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