Novel approaches to optically active substituted 4,5-dihydro-1,2,4-triazin-6(1H)-ones as conformationally constrained peptidomimetics

Synthesis of 4,5-dihydro-1,2,4-triazin-6-ones bearing different chiral ol-a mino acid residues at the C3 and N1 positions is reported. Cyclocondensatio n of N-thioacylphthalimides with a-amino hydrazides afforded C3 functionali sed dihydrotriazinones in good yields without detectable epimerisation. Mor eover, N1-alkylation of the dihydrotriazinone ring with several ol-bromo es ters was performed with satisfactory yields. Interestingly, this alkylation reaction was found to be regioselective with respect to N4 and NHBoc. This class of compounds represents a new series of small conformationally const rained peptide derivatives.