Synthesis and conformational study of poly(N delta-carbobenzoxy, N delta-benzyl-L-ornithine) and poly(N delta-benzyl-L-ornithine).

Abstract

AbstractPoly(Nδ‐carbobenzoxy, Nδ‐benzyl‐L‐ornithine) (PCBLO) was prepared by the standard NCA method. PCBLO was converted into poly(Nδ‐benzyl‐L‐ornithine) (PBLO) through decarbobenzoxylation with hydrogen bromide. The monomer Nδ‐benzyl‐L‐ornithine was synthesized by reacting L‐ornithine with benzaldehyde, followed by hydrogenation. The conformation of the two polypeptides was studied by optical rotatory dispersion and circular dichroism. PCBLO forms a right‐handed helix in helix‐promoting solvents. In mixed solvents of chloroform and dichloroacetic acid (DCA) it undergoes a sharp helix–coil transition at 12% (v/v) DCA at 25°C, as compared with 36% for poly(Nδ‐carbobenzoxy‐L‐ornithine) (PCLO). Like PCLO, the helix–coil transition is “inverse,” that is, high temperature favors the helical form. PBLO is soluble in water at pH below 7 and has a “coiled” conformation. In 88% (v/v) 1‐propanol above pH (apparent) 9.6 it is completely helical. In 50% 1‐propanol the transition pH (apparent) is about 7.4; this compares with a pHtr of about 10 for poly‐L‐ornithine in the same solvent.