摘要:
Cyclic hexapeptides in which the adjacent N(epsilon)-nitrogens of cyclo-(Lys-Lys-Gly)2 are cross-linked by p-xylyl or (CH2)6 units have been prepared. The key steps in the syntheses of these novel types of peptide were the use of tosyl (or, less efficiently, trifluoroacetyl) as N(epsilon)-protection that allowed intramolecular cross-linking of the tripeptides Boc-Lys(R)-Lys(R)-Gly-OMe (R = Ts or CF3CO) using alpha,omega-dibromo-alkanes/ Cs2CO3, and the efficient cyclo-dimerisation of the pentafluoro-phenyl esters of the resultant cross-linked tripeptides.