Abstract: Four novel organophosphorus compounds: N-diethylphosphoryl benzoxazolone(DEPBO), N- (2-oxo-1, 3, 2-dioxaphosphorinanyl)-benzoxazolone (DOPBO), 3- [O- (2-oxo-1, 3, 2-dioxaphosphorinanyl)-oxy]-1, 2, 3-benzotriazin-4 (3H)-one (DOPBT) and 3-(di-ethylphosphoryl-oxo) -1, 2, 3-benzotriazine-4 (3H)-one (DEPBT) have been studied for pep-tide synthesis.All of the four compounds are stable colourless crystal which can be easilyprepared in large quantity.We have synthesized a number of bioactive peptides such as ana-logues of delta sleep inducing peptide, a cyclic heptapeptlde isolated form Caryophyllaceae,etc.by using these organophosphorus compounds as coupling reagents in both solution andsolid phase peptide synthesis.In the coupling reaction, the hydroxy group in amino compo-nent does not need to be protected and the dehydration of asparagine which is easily causedby DCCor EDCwas not observed.We have also compared our organophosphorus com-pounds with other coupling reagents such as DCC/HOBt, BOP, etc.In terms of reactionyield, our compounds are as good as other commonly used coupling reagents.Among thefour compounds, DEPBTgives the best results.As far as the racemization is concerned, es-pecially in the hindered coupling or in the cyclization, DEPBTis much better than the oth-ers.

Key words: Organophosphorus reagent, Coupling reagents, Bioactive peptides, Cyclopeptide