New caulerpenyne-derived metabolites of an Elysia sacoglossan from the South Indian coast.
Chemical analysis of the secondary metabolite pattern of the sacoglossan mollusc Elysia cf. expansa, collected along South Indian coasts, showed the presence of the typical Caulerpa-derived sesquiterpene caulerpenyne (1) and two new minor co- occurring metabolites, the compounds dihydrocaulerpenyne (4) and expansinol (5). The chemical characterization of these molecules, structurally related to 1, is reported.
Further syphonosides from the sea hare Syphonota geographica and the sea-grass Halophila stipulacea
Abstract The unusual structural features of syphonoside ( 1 ), recently reported from the marine mollusc Syphonota geographica and its prey Halophila stipulacea , stimulated further investigations on the minor secondary metabolites of both organisms. The three novel macrocyclic glycoterpenoids 2 – 4 , structurally related to the main co-occurring metabolite 1 , have been isolated and chemically characterized mainly by NMR spectroscopic techniques and degradation methods. Compounds 2 and 3 were found only in the mollusc whereas compound 4 was isolated in trace quantities exclusively from the sea-grass.
Synthesis of 2,4-dideoxy-.beta.-D-erythro-hexopyranosyl nucleosides
The synthesis of 1-(2,4-dideoxy-β-D-erythro-hexopyranosyl)thymine (12) 1 was accomplished using two different synthetic routes. It was obtained starting either from 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose or from tri-O-acetyl-D-glucal. The other modified nucleosides, with either a cytosine, guanine, or adenine moiety, were synthesized using the second reaction scheme. Deoxygenation reactions were accomplished with the (2,4-dichlorophenoxy)thiocarbonyl derivatives generated in situ