First report of bioactive sterols from the muricid gastropod Chicoreus ramosus

Two unusual △⁵ sterols with unprecedented skeletons were isolated from the organic extract of muricid gastropod Chicoreus ramosus collected off the Gulf of Mannar Coast. This is the first report of isolation of bioactive sterols endowed with anti-inflammatory potentials from this species. The compounds were characterized as (5Z)-24a-homo-cholesta-5,24a¹(24a²) dien-3β-ol (1) and 27(25 → 23)-abeo-(5Z)-3β-hydroxy-24-isopropyl cholesteno-26,23-lactone (2) by the interpretation of a series of spectroscopic techniques involving two-dimensional nuclear magnetic resonance and mass spectral data. The compound 1 is unusual in that it has an ethylene attachment stemming from the additional methylene group at the 24a position of the steroid side chain, whereas compound 2 has a unique side chain bearing a γ-valerolactone ring. The △⁵ sterol bearing ethylene group (1) displayed comparatively better antidiabetic activity as characterized by inhibitory effects towards α-amylase and α-glucosidase enzymes (IC₅₀ 1.97 mM and 1.78 mM, respectively), whereas the cholestenolactone analogue (2) manifested higher anti-inflammatory activity (IC₅₀ 1.42 mM) as determined by in vitro 5-lipoxygenase inhibitory potential. Structure-activity correlation study showed that the biological activities of the studied sterols were directly related to their electronic properties. The homosterol (1) exhibiting improved antidiabetic properties showed higher lipophilic character coupled with lesser steric restrictions.