GUANIDYL DERIVATIVE

PROBLEM TO BE SOLVED: To obtain a new guanidyl derivative, having excellent suppressing actions on the Maillard reaction and antioxidant actions in combination and further high safety and useful for treatment and/or prevention of diabetic complications, atherosclerosis, etc. SOLUTION: This guanidyl derivative of formula I Z is S, O or NR (R" is H or a 1-4C alkyl); R is H, a 1-4C alkyl or a 2-5C acyl; A is a single bond, a 1-8C alkylene, etc.; ring D group is a group of formula II [R is H, a 1-4C alkyl or a 2-5C acyl; (1) is 0 or 1-10; R is a 1-4C alkyl; (p) is 0 or 1-2], formula III [R is a 1-7C alkyl, a halogen, etc.; (m) is 0 or 1-5] or formula IV [R is a 1-7C alkyl, phenyl, etc.; (n) is 0 or 1-3, etc.]} or its acid addition salt, e.g. a compound of formula V is cited. For example, the compound of formula V is obtained by using a compound prepared from a 3,5-di-t-butyl-4- hydroxybenzaldehyde and methyl triphenylphosphoranylideneacetate as a starting raw material through several steps.