| abstract |
A polyethylene glycol derivative of the formula ##STR1## wherein R represents a lower alkyl and n represents an optional positive integer which renders the average molecular weight of the polyethylene glycol moiety about 1,000 to 12,000, a peptide modified by said polyethylene glycol derivative and a method for production thereof. The polyethylene glycol derivative (I) is capable of modifying the guanidino groups in peptides. The peptides modified by the polyethylene glycol derivative (I) are extremely stable, are considerably delayed in biological clearance (i.e. the durability is extended) and exhibit their physiological activities effectively over the long period. |