COMPLEXES OF TRYPTOPHAN DIPEPTIDES WITH THE R(2)SN(IV)(2- SPECTROSCOPIC STUDIES, SOLUTION PROPERTIES AND STRUCTURAL IMPLICATIONS() ION (R=ME, PH) )

Tryptophan dipeptides such as L-tryptophyl-L-alanine (H(2)TrpAla), L-t ryptophyl-L-tyrosine (H(2)TrpTyr), L-tryptophyl-L-tryptophan (H(2)TrpT rp), along with L-histidyl-L-tyrosine (H(2)HisTyr), were reacted with R(2)SnO (R = Me, Ph) yielding the corresponding complexes. The complex es have been characterized by IR and Sn-119 Mossbauer spectroscopy in the solid state and by H-1 and C-13 NMR in CD3OD solutions. Monomeric species were detected, with the tin atom arranged in a pentacoordinate d trigonal-bipyramidal structure. The dipeptides are coordinated via t he terminal amino group, deprotonated peptide nitrogen and terminal ca rboxylate group. No side-chain appears to be involved in bonding. Dete rmination of rotamer populations for selected compounds was accomplish ed by vicinal coupling constant analysis and side-chain orientations a re interpreted. In this connection, the potential applications of thes e compounds as drugs is discussed.