BIOSYNTHESIS OF THE CYCLOHEXANECARBOXYLIC ACID STARTER UNIT OF OMEGA-CYCLOHEXYL FATTY-ACIDS IN ALICYCLOBACILLUS-ACIDOCALDARIUS

The formation of the cyclohexanecarboxylic acid starter unit of omega-cyclohexyl fatty acids from shikimic acid in Alicyclobacillus acidocaldarius (formerly Bacillus acidocaldarius) has been studied. Feeding experiments with C-13- and H-2-labeled samples of shikimic acid and potential intermediates in the wild type and two blocked mutants demonstrated that the formation of cyclohexanecarboxylic acid in this organism follows the same pathway as in Streptomyces collinus (J. Am. Chem. Soc., preceding paper in this issue). (1S,3S)-3-Hydroxycyclohexanecarboxylic acid (20) is accumulated by blocked mutant 2, indicating that 5-hydroxycyclohex-1-enecarboxylic acid (6) is first reduced to the hydroxy acid 20 and then dehydrated to 2-cyclohexenecarboxylic acid (8). A sample of [6-H-2(1)]shikimic acid was fed to blocked mutant 2. Deuterium occupied the pro-2S position in the resultant 20, which was then lost when 20 was refed to blocked mutant 10. Thus, the dehydration of 20 involves the removal of the nonacidic pro-2S proton and the C-3 hydroxyl group in an anti fashion. The stereochemistries of other transformations along the pathway are also discussed.