Long-chain 2H-Azirines with heterogeneous terminal halogenation from the marine sponge Dysidea fragilis

摘要

Three new omega-halogenated long-chain 2H-azirines were isolated from the sponge Dysidea fragilis. Their structures revealed heterogeneity in both the composition of the terminal 1,1-dihalo-vinyl group and enantiomeric ratios at C2 of the azirine-2-carboxylate ester terminus. Azirine-2-carboxylate esters were shown to racemize spontaneously. A hypothesis is proposed for the biosynthesis of the azirinecarboxylate family of natural products that involves enzyme-catalyzed free radical halogenation followed by elimination of hydrohalic acid.