Fa. Robey, Selective and facile cyclization of N-chloroacetylated peptides from the C-4 domain of HIV Gp120 in LiCl/DMF solvent systems, J PEPT RES, 56(3), 2000, pp. 115-120
Lithium salts have been reported to mediate the solubilization of peptides
in organic solvents in 1989 (Seebach, D., Thaler, A. & Beck. A. K. Helv. Ch
im. Acta 1989; 72, 857-867). The use of Li salts in an organic solvent to i
nfluence cyclization of a reactive peptide that only polymerizes in an aque
ous solvent, has not been reported. Here, the selective and facile cyclizat
ion of N-chloroacetylated, C-cysteine amide peptides from the C4 domain of
HIV-1 gp120 in LiCl/DMF solvent systems is demonstrated. The addition of st
oichiometric amounts of Tris base to 1 mg/mL peptide in LiCl/DMF solutions
was sufficient to drive the cyclization to completion within 3 h at ambient
temperatures. Cyclic peptides were the only detectable reaction products a
nd these were confirmed using reversed-phase HPLC and mass spectrometric an
alyses of the final products. In aqueous solutions at pH 7.4, only polymers
were obtained as judged by HPLC and SDS-PAGE. The method of using Li salts
in an organic solvent to enhance the cyclization of unprotected amphipathi
c peptides may be useful in many situations beyond those described here.