合成路线1

The cyclic peptide precursor (XIV) was prepared by solid-phase synthesis on a preformed HMPB-MBHA resin. Attachment of N-Fmoc-glycine (I) to the resin by means of DCC and DMAP afforded resin (II). The Fmoc protecting group was then removed with piperidine in DMF, yielding the glycine-bound resin (III). Further couplings with the following protected amino acids: N-Fmoc-3-(aminomethyl)-5-nitrobenzoic acid (IV), N-Fmoc-L-tyrosine(O-t-butyl) (VI) and N-Fmoc-glycine (I), followed by Fmoc deprotection cycles, produced in turn the peptide resins (V), (VII) and (VIII). To peptide resin (VIII) was then coupled N-Fmoc-L-aspartic acid gamma-t-butyl ester (IX), yielding resin (X). Peptide (XI) was then liberated from the resin by means of 1% trifluoroacetic acid in CH2Cl2. The Fmoc group was subsequently removed by treatment with diethylamine in acetonitrile, giving (XII).