CONFORMATIONALLY CONSTRAINED ANALOGS OF DIACYLGLYCEROL - INTERACTION OF GAMMA-LACTONES WITH THE PHORBOL ESTER RECEPTOR OF PROTEIN-KINASE-C

Four 2-deoxy-erythro-1,4-lactones in the D- and L-series and the four corresponding 2-deoxy-threo-1,4-lactones, bearing myristic acid acyl groups at either primary or secondary alcohol functions, were synthesized from L-ascorbic and D-isoascorbic acids. These eight pentonolactones which represent all possible isomers in this series were designed as rigid analogues of 1,2-diacylglycerol (DAG). The inhibition by these compounds of the binding of [H-3]phorbol-12,13-dibutyrate to protein kinase C (PK-C) demonstrated the importance in this context of stereochemistry and particularly of the orientation of the fatty acid side chain. The most effective inhibitor (13d, K(i) = 2.3-mu-M) has a fixed conformation which is presumed to be similar to the conformation adopted by DAG when binding to PK-C. A three-point attachment model which has been previously used to rationalize the similar behavior of DAG and phorbol esters was extended to include additional points of equivalence between these two PK-C agonists. This extended model addresses the disposition of the lipophilic myristic acid side chain and the orientation of the lactone carbonyl group which functions as a hydrogen bond acceptor. In this new model, the most active isomer 13d provides the best fit of the eight pentonolactones to phorbol myristate acetate.