Abstract
Cyclopeptides containing a functionalized meta-aminobenzoic acid residue ( m-aB[CH 2X] with X = OC 6H 5, OAc, Br, C1) linked to a tetraglycyl-phenylalanyl sequence, have been synthesized in solution. A phenyl ether group has been used during chain elongation and cyclisation, and then cleaved by treatment with HBr/HOAc to give the corresponding bromide, from which the acetate and the chloride have been obtained. The functionalized aminobenzoic acid residues possess a latent quinonimmonium methide electrophilic function, and these cyclopeptides are potential “suicide” substrates of chymotrypsin-like proteases. The cyclopeptides with X = Br or Cl irreversibly inhibit α-chymotrypsin ( k inact K I = 180 M −1min −1 for X = Cl ). The compounds with poorer leaving groups X = OAc or OC 6H 5 are devoid of inactivating effect and only behave as substrates of this enzyme ( k cat K M = 31 800 M −1min −1 and 120 000 M −1min −1, respectively).
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