Chemical synthesis and in vitro biological evaluation of a phosphorylated bisubstrate inhibitor of type 3 17beta-hydroxysteroid dehydrogenase.

Type 3 17beta-hydroxysteroid dehydrogenase (17beta-HSD) catalyzes the last step in the biosynthesis of the potent androgen testosterone (T) by selectively reducing the C17 ketone of 4-androstene-3,17-dione (delta4-dione), with NADPH as cofactor. This enzyme is thus an interesting therapeutic target for androgen-sensitive diseases. Using an efficient convergent chemical approach we synthesized a phosphorylated version of the best delta4-dione/adenosine hybrid inhibitor of type 3 17beta-HSD previously reported. An appropriately protected C2' phosphorylated adenosine was first prepared and linked by esterification to the steroid delta4-dione bearing an alkyl spacer. After three deprotection steps, the phosphorylated bisubstrate inhibitor was obtained. The inhibitory potency of this compound was evaluated on homogenated HEK-293 cells overexpressing type 3 17beta-HSD and compared to the best non-phosphorylated bisubstrate inhibitor. Unexpectedly, the phosphorylated derivative was slightly less potent than the non-phosphorylated bisubstrate inhibitor of type 3 17beta-HSD. Two hypotheses are discussed to explain this result: 1) the phosphorylated adenosine moiety does not interact optimally with the cofactor-binding site and 2) the bisubstrate inhibitors, phosphorylated or not, interact only with the substrate-binding site of type 3 17beta-HSD.