a lower acyloxy group (e.g., a C2 -C4 acyloxy group) or a lower alkyl (e.g., C1 -C3 alkyl) group substituted with sulfonic acid or an alkali metal salt thereof, with the proviso that when R3 is a methyl group, X is not a cyano group, 2-ketopyrrolidinyl group, a lower alkoxy group, a lower acyl group, a lower acyloxy group or a lower alkyl group substituted with sulfonic acid or a salt thereof; M1