Conformational Analysis, Thermal Rearrangement, and EI‐MS Fragmentation Mechanism of (1(10) E ,4 E ,6 S ,7 R )‐Germacradien‐6‐ol by 13 C‐Labeling Experiments

An uncharacterized terpene cyclase from Streptomyces pratensis was identified as (+)‐(1(10) E ,4 E ,6 S ,7 R )‐germacradien‐6‐ol synthase. The enzyme product exists as two interconvertible conformers, resulting in complex NMR spectra. For the complete assignment of NMR data, all fifteen ( 13 C 1 )FPP isotopomers (FPP=farnesyl diphosphate) and ( 13 C 15 )FPP were synthesized and enzymatically converted. The products were analyzed using various NMR techniques, including 13 C,  13 C COSY experiments. The ( 13 C)FPP isotopomers were also used to investigate the thermal rearrangement and EI fragmentation of the enzyme product.