Styrene derivatives and salts thereof

A styrene derivative represented by the formula (1) or a salt thereof:

• ##STR141## wherein R.sub.1 and R.sub.2 are the same or different and each is a hydrogen atom, a lower alkoxy group, a halogen atom or a lower alkyl group;
• R.sub.3 are the same or different and each is a hydroxy group, a lower alkoxy group, a lower alkyl group, a lower alkoxycarbonyloxy group, a lower acyloxy group, a di-loweralkyl phosphate or an amino acid which may have a protective group;
• l is an integer of 0 to 5;
• m is an integer of 0 to 5;
• X represents a formula --N(Z)CO-- {wherein Z represents a formula (CH.sub.2).sub.n A (wherein A represents a hydrogen atom, a carboxyl group, a di- or mono-loweralkylcarbamoyl group, a carbamoyl group, a lower alkoxycarbonyl group, a cyano group, a lower alkoxy group, a N-acylamino group, a phenyl group which may be substituted, a pyridyl group or a thienyl group, n is an integer of 0 to 5)} or a single bond, Y represents --C(Z').dbd.CH--, --CH.dbd.CH--C(Z').dbd.CH--, --C(Z').dbd.CH--CH.dbd.CH-- (wherein Z' is the same as Z), provided that when n=0, both Z and Z' are not hydrogen atoms, and that when l is O, X represents a single bond.