Discovery of novel trimethylalkanes in the internal hydrocarbons of developing pupae of Heliothis virescens and Helicoverpa zea

Novel trimethyl-branched alkanes which eluted with the monomethylalkanes we re identified in the internal lipids of Helicoverpa zea but were not presen t in Heliothis virescens. Their structures were unique in that the first me thyl branch occurred on carbon 2 and the 2nd and 3rd methyl branch points w ere separated by a single methylene. Novel trimethylalkanes identified from their chemical ionization and electron impact mass spectra were 2,18,20-tr imethyltetratriacontane, 2,18,20-trimethylhexatriacontane, and 2,24,26-trim ethyldotetracontane. Previous reports did not find these trimethylalkanes i n the cuticular surface lipids of larvae, pupae or adults of either species . The internal pupal hydrocarbons of H. virescens and H. zea amounted to 12 3 mug and 304 mug per pupa, respectively. They consisted of n-alkanes (8 an d 4%, respectively) and methyl-branched alkanes (88 and 94%, respectively). The n-alkanes ranged in chain length from approximately 21 to 35 carbons a nd the methyl-branched alkanes from approximately 26 to 55 carbons vs. meth yl-branched alkanes from 28 to 37 carbons previously reported for hydrocarb ons from the pupal cuticular surface. The major n-alkane was heptacosane (3 .3 and 1.2%, respectively, in H. virescens and H. zea). The major methyl-br anched alkanes in H. virescens were methylhentriacontane (15%), methyltritr iacontane (12%) and dimethyltritriacontane (10%), and in H. zea were methyl nonacosane (17%), dimethylnonacosane (9%) and methylhentriacontane (20%). E xcept for the novel trimethylalkanes, the methylalkane branch points were p redominantly on odd-numbered carbons as has been reported for these and oth er species. (C) 2001 Elsevier Science Inc. All rights reserved.