A new sesquiterpene synthase from Streptomyces lincolnensis was identified as isoishwarane synthase. The absolute configuration of its product was determined by an enantioselective deuteration strategy. The cyclisation mechanism from farnesyl diphosphate to isoishwarane was studied in incubation experiments with various isotopically labelled substrates and by site-directed mutagenesis. GC/MS analysis of all 15 isotopomers of (13C)isoishwarane also gave insights into the EI-MS fragmentation mechanism.
