enantiopure 2-methyloct-(6E)-enoic acids. The 5S,6R,9S isomer has NMR spectra and optical rotation identical with those of the natural compound. A bis-azide-tagged penicillenol analogue was also synthesized for photoaffinitylabeling of target proteins. The photolysis of the bis-azide in the presence of methanol as a protein-mimicking nucleophile led to reaction only of the aryl azide, while leaving the