Methods for producing phenylalanine derivatives having a quinazolinedione skeleton and intermediates for production thereof

The present invention provides a method for producing a phenylalanine derivative(s) having a quinazolinedione ring of formula (5), including steps comprising of reacting an acylphenylalanine derivative(s) of formula (1) with a carbonyl group-introducing reagent(s) and a derivative(s) of anthranilic acid to form an asymmetric urea intermediate(s); making the asymmetric urea intermediate(s) into a quinazolinedione compound(s) of formula (4) in the presence of a base(s); and N-alkylating quinazolinedione ring amide of the obtained quinazolinedione compounds with N-alkylation agents. This production method is an industrially applicable method for producing phenylalanine derivatives having a quinazolinedione skeleton, which are compounds highly useful as drugs having α 4 integrin inhibiting activity. In the formulae (1) and (5), R1 represents a phenyl group having a substituent(s) and the like, R2 represents an alkyl group and the like, R3 represents a dialkylamino group and the like, and R4 represents an alkyl group and the like.