Conformational analysis of serricornin: Application of molecular mechanics calculations to stereochemical assignment of serricornin, sex pheromone of cigarette beetle (Lasioderma serricorne F.).

Conformational analysis using molecular mechanics (MM) was performed for a determination of the stereochemistry of serricornin, the sex pheromone of the cigarette beetle (Lasioderma serricorne F.). An exhaustive conformational analysis using MM2 calculations with algorithms for covering torsional energy surfaces of flexible molecules furnishes coordinates and steric energies of all local energy minimum conformers of serricornin, both acyclic and the corresponding cyclic forms. These coordinates gave angles required for the calculation of vicinal H/H coupling constants ((3) J HHs) of each energy minima by Altona's modified Karplus equation. The Boltzmann distributions of all local energy minima were calculated from their steric energies to furnish populations of each energy minimum conformer. Populationweighted averaged(3) J HHs of four enantiomeric pairs, (S (*),S (*),S (*))-, (S (*),S (*),R (*))-, (S (*),R (*),S (*))-, and (R (*),S (*),S (*))-serricornins were calculated from the data above. The observed(3) J HHs of the naturally occurring serricornin, both acyclic and cyclic forms, are fitted best to calcd.(3) J HHs of (4S (*), 6S (*), 7S (*))-acyclic and (3S (*), 5S (*), 6S (*))-cyclic serricornin, respectively, among those of four enantiomeric pairs of serricornin.