Dipeptide isosteres. 1. Synthesis of dihydroxyethylene dipeptide isosteres via diastereoselective additions of alkyllithium reagents to N,N-dimethylhydrazones. Preparation of renin and HIV-1 protease inhibitor transition-state mimics

Abstract

The amino and diamino dihydroxyethylene dipeptide isosteres 19a,b and 23 are important intermediates for the preparation of inhibitors of human renin and HIV-1 protease, respectively. A general synthetic strategy was developed to access both dipeptide isosteres. The key step was a diastereoselective addition of an alkyllithium reagent to an aldehyde hydrazone. Thus, isosteres 19a and 19b were synthesized by addition of either benzyllithium or (cyclohexylmethyl)lithium to (4S,5R)-2,2-dimethyl-4-(2-methylpropan-1-yl)-5-formyl-1,3-dioxolane N,N-dimethylhydrazone (4) in dietbyl ether at -10 o C. The hydrazine addition product was reduced to the amine, and the acetonide protecting group was removed