Marine sterols

Fig. 7. Structural diversity of marine sterols where R — a variety of unique side chains, including (a) cyclopropa(e)ne, (b) acetylene, (c) polyalhylated, and (d)...

The surge of interest in marine sterols, stimulated by some several hundred new and unique sterol structures found in marine invertebrates over the last two... 

It has been suggested [6] that these unusual sterols, especially in those cases where these unusual sterols comprise the entire sterol content of the organisms, likely replace conventional sterols as cell-membrane components. Evidence for this comes from subcellular fractionation and subsequent analysis of two marine sponges [10]. The sterol composition of the membrane isolates was found to be identical to that of the intact sponge. Most common variation of the marine sterol is in the side-chain, situated deep in the lipophylic environment of the phospholipid bilayer. This suggests that unusual fatty acids might accompany the sterols, and indeed this is often the case [8]. 

Ballantine, J.A. Lavis, A. Roberts, J.C. Morris, R.J. (1977) Marine sterols. V. Staol of some tunicata. The occurrence of saturated ring sterols in these filter-feeding aganisms. J. Exp. Mar. Biol. Ecol., 30,29-44. 

Bonini, C. Kinnel, R.B. Li, M. Scheu, P.J. Dja assi, C. (1983) Isolation, structure elucidation and partial synthesis of papakusterol, a new biosynthetically imusual marine sterol with a cyclopropyl-containing side chain. Tetrahei-on Lett., 24,277-80. 

Intramolecular alkylation has been used in the synthesis of the cyclopropane side chain of the marine sterols Glaucasterol95 and Petrosterol96. During the preparation of the latter the mesylate 1 was reacted with 1.0 equivalent of potassium-tcr -butoxide in tetrahydrofuran/ben-zene at 0°C to give the trans-substituted cyclopropane 2 in >70% yield. 

Additional unusual steroid derivatives have been isolated from marine sponges, eg., polymastiamides, steroid/aminoacid conjugates isolated from Polymastia boletiformis, a Norwegian marine sponge [180], and an aminoimidazolium salt of steroid trisulfate from Topsentia sp. [181], Some of these marine sterols are being reproduced by chemical synthesis in the laboratory [182],... 

The first examples of marine sterols with the sulfamate ester functionality were haplosamates A and B (462 and 463), which were obtained from two sponges from the Philippines, a Xestospongia sp. (Haplosclerida, Petrosiidae) and an unidentified haplosclerid sponge [355]. The structures of haplosamates A and B were determined by interpretation of spectral data and the compounds were found to inhibit HIV-1 integrase with IC50 values of 50 pg/ml and 15 ig/ml, respectively. 

Marine Sterols. Several hundred unique sterol structures have been elucidated from a variety of marine invertebrates. A single nucleus can be used to describe most terrestrial sterols, but no single template suffices for marine sterols, Similar to cholesterol, marine sterols play a critical role in both the physiology and biochemistry of biological systems. 

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