The invention relates to N-sulfonyl-α-amino-acetic acid derivatives of the general formula (I): including the optical isomers thereof and mixtures of such isomers, wherein Ar1 and Ar2 independently of each other stand for an optionally substituted aryl or heteroaryl group, R1 and R2 stand independently of each other for hydrogen, optionally substituted C1-C5alkyl, optionally substituted C2-C5alkenyl, C-2C5alkynyl or optionally substituted C3C6Cycloalkyl; R3 designates hydrogen, C-3C5alkenyl, C3-C5 alkynyl or optionally substituted C1-C5alkyl; R4 is optionally substituted C1-C5alkyl, optionally substituted C-2C5alkenyl, C-2C5aklynyl or optionally substituted C-3C6 cycloalkyl; R5 and R6 are independently of each other hydrogen or optionally substituted C1-C5alkyl, optionally substituted C2-C5alkenyl, C-2C5alkynyl or optionally substituted C3-C6cycloalkyl; R7 and R8 are independently of each other hydrogen or optionally substituted C1-C5alkyl, optionally substituted C2-C5alkenyl, C2-C5alkynyl or optionally substituted C3-C6cycloalkyl; W designates a bridge selected from —O—, —S—, —SO—, —SO2— or is an —NH— or —N(C1-C5alkyl)-bridge; X designates a direct bond or a bridge selected from —O—, —S—, —SO—, —SO2— or is an —NH or —N(C1C5alkyl)-bridge; Y designates —OR9 or NR10R11; a and b independently of each other stand for a number 1, 2 or 3; and c stands for a number zero, 1 or 2; with R9, R10 and R11 being defined according to the claims. These compounds possess useful plant protecting properties and may advantageously be employed in agricultural practice for controlling or preventing the infestation of plants by phytopathogenic microorganisms, especially fungi.