Low racemization peptide coupling reagent , introduced by Castro, analogous to BOP Reagent (1H-Benzotriazol-1-yl-oxytris(dimethyl-amino)-phosphonium hexafluorophosphate) but avoiding the formation of the carcinogenic HMPA as a by-product: Tetrahedron Lett., 31, 205 (1990). For use in formation of mixed phosphonate diesters, see: J. Org. Chem., 60, 5214 (1995).