Polyketide origin of pheromones of Carpophilus davidsoni and C-mutilatus (Coleoptera: Nitidulidae)

Biosynthesis of pheromones from Carpophilus davidson Dobson and C. mutilatus Erichson was investigated by feeding the beetles diets containing isotopically substituted (C-13 and deuterium) fatty acids and then analyzing the resulting labeled pheromone components. (2E,4E,6E,8E)-7-Ethyl-3,5-dimethyl-2,4,6,8-undecatetraene, (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6,8-undecatetraene and (2E,4E,6E)-5-ethyl-3-methyl-2,4,6-nonatriene from C. davidsoni and (3E,5E,7E)-5-ethyl-7-methyl-3,5,7-undecatriene from C. mutilatus were abundant enough to be analyzed by both NMR spectroscopy and MS. Eleven additional minor analogues were analyzed only by MS. Each hydrocarbon can be assembled from just three different acyl units: The initial unit can be acetate, propionate or butyrate. Propionate is the second unit in all of the analogues encountered so far, extending the chain by two carbons and producing a methyl branch. Subsequent chain-extending units can be either propionate or butyrate, leading to additional methyl or ethyl branches, respectively. The final acyl unit is either propionate or butyrate and it loses its carboxyl carbon during hydrocarbon biosynthesis. A hydrocarbon with four total units is a triene and one with five is a tetraene. Assembly is proposed to be as in usual fatty acid anabolism, except that other precursor units are used in addition to acetate and that the double-bond reduction step of each chain-elongation cycle does not occur, leaving the conjugated, unsaturated system. Seven of the analyzed hydrocarbons were not previously known to occur in C. davidsoni; two of these are novel: (2E,4E,6E,8E)-5,7-diethyl-3-methyl-3,4,6,8-undecatetraene and (2E,4E,6E)-3,5-dimethyl-2,4,6-octatriene.