To provide an immunosuppressant.
The immunosuppressant comprises a pterin derivative represented by formula (I) [R1 and R2 are each a 1-20C alkyl group which may be substituted with one or more groups selected from a group consisting of OH, an amino group, a phosphoric acid group and a sulfonic group, an acyl group represented by the formula R3-CO (R3 is a 1-4C alkyl group), an amino acid residue represented by formula (a) or H; R4 is H or a 1-4C alkyl group or a 1-4C alkyl group substituted with one group selected from OH, a carboxyl group, a carbamoyl group, a mercapto group, a methylthio group, an amino group, a guanidine group, an imidazolyl group, a phenyl group, a hydroxyphenyl group and an indolyl group; X is a formyl group or a hydroxymethyl group; A is a group represented by formula (Ia); n is 0 or an integer of ≥1)] or its cyclic substance or its salt.
MAKINO KEISUKE
YAMASHITA KOHEI
SASADA MASATAKA
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