NEW MATERIAL: A compound of formula [R1 is H or a protecting group; R2 and R3 are H, alkyl, aryl, COOR4 (R4 is H, alkyl, alkenyl or the like), or the like with the proviso that one of them is COOR4; R5 is OH when R3 is COOR4, and is H, alkyl, aryl or the like when R2 is COOR4; R6 and R7 are each H, OH, alkoxy, alkyl, aryl or the like; B is phenyl, 5-6 membered heteroaryl ring; X is (CH2)n (n is 0-2), OCH2, NHCH2, SOCH2 or the like; A is OPO3R8R9 (R8 and R9 are each H, alkyl, alkenyl or the like), BO2R8R9, tetrazole, or the like].

EXAMPLE: 1,2,3,4-Tetrahydro-5-phosphono-3-isoquinoline carboxylic acid.

USE: Effectively used for the medical treatment of a disease relating to the blockade of stimulus concentrated amino acid receptor.

PROCESS: A solution of dimethyl 5-(diethoxyphosfinyl)-3,4-dihydro-2,3(1H)- isoquinoline dicarboxylate, is heated under the reflux, to obtain the compound of the example.