SYNTHESIS AND CHARACTERIZATION OF NEW PHOTOLABILE PHORBOL ESTERS FOR AFFINITY LABELING OF PROTEIN KINASE C

Three new photolabile phorbol esters (3, 6, and 9) with a diazoacetyl group at positions 3, 12, and 13, respectively, have been synthesized from phorbol (1a) and found to bind with significant affinity to the peptide (peptide C) incorporating the phorbol ester-binding domain of protein kinase C. As required for its use as a protein kinase C receptor probe, the solution photochemistry of 3 led predominantly to insertion products. Tritium labeling of these probes at C-20 was accomplished by oxidation with activated manganese dioxide to the C-20 aldehyde and subsequent 3H-labeled sodium borohydride reduction. Initial affinity labeling studies showed that probes 6 and 9 labeled peptide C, suggesting that the introduction of a photolabile group into position 12 or 13 of the phorbol esters could be used to identify the structural features of PKC involved in its binding to activators.