CHARCOAL SURFACE-ASSISTED CATALYSIS OF INTRAMOLECULAR DISULFIDE BOND FORMATION IN PEPTIDES

A mild and highly efficient method for intramolecular disulfide bond f ormation in peptides mediated by charcoal has been developed. Completi on of the charcoal-assisted catalysis of disulfide bond formation took less than 6 h, testing a series of peptides with ring sizes varying f rom 2 to 17 amino acids. Kinetic studies revealed that the formation o f small and large intramolecular disulfide cycles especially was accel erated significantly by the aid of charcoal as compared with dimethyl sulfoxide-and air-mediated cyclization. Oxygen adsorbed onto the charc oal surface is a prerequisite for disulfide bond formation. Thermodyna mic studies showed that cyclization is accelerated by reduction of ent ropy of the peptides, most likely because of transient adsorption to t he charcoal surface, thus resulting in a lower activation energy. (C) Munksgaard 1998.