1965 Volume 38 Issue 12 Pages 2139-2144
A cyclic decapeptide, cyclo-(L-valyl-L-ornithyl-L-leucyl-D-phenylalanylglycyl)2, has been synthesized in an attempt to obtain information about the relation of the structure to the antibacterial activity of gramicidin S.
The synthesis of the cyclic decapeptide was achieved in two ways. The condensation of p-methoxybenzyloxycarbonyl-L-valyl-δ-benzyloxycarbonyl-L-ornithyl-L-leucyl-D-phenylalanylglycine azide with L-valyl-δ-benzyloxycarbonyl-L-ornithyl L-leucyl-D-phenylalanylglycine afforded the corresponding N-blocked decapeptide, which was converted to the p-nitrpohenyl ester by the action of di-p-nitrophenyl sulfite. After the p-methoxybenzyloxycarbonyl group had been removed with trifluoroacetic acid, the decapeptide p-nitrophenyl ester was transformed to the cyclic benzyloxycarbonyl-substituted decapeptide by treatment with pyridine. On the other hand, this compound was also obtained by a dimerization reaction of L-valyl-δ-benzyloxycarbonyl-L-ornithyl-L-leucyl-D-phenylalanylglycine p-nitrophenyl ester. In the latter case, however, the yield was poor. The cyclic benzyloxycarbonyl-substituted decapeptide was hydrogenated in the presence of palladium black to give the desired cyclic decapeptide dihydrochloride.
The effects of the synthesized cyclic decapeptide on bacterial growth have also been examined. It was observed that the compound was about ten times as active as gramicidin S against B. subtilis in a synthetic medium; however, it showed silghtly less activity than gramicidin S in a bouillon agar medium.
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