The present invention provides actagardine, actagradine B and deoxy actagardine B derivatives of formula (I), wherein: X1 denotes that the residue is Leu； Val； or Ile； X2 denotes that the residue is Leu； Val； or Ile； R1 represents an alkyl or heteroalkyl group, substituted by at least one hydroxyl substituent, and R2 represents hydrogen, or an alkyl or heteroalkyl group, optionally substituted by at least one hydroxyl substituent, or R1 and R2 taken together with the nitrogen atom represent a heterocyclic group having at least one hydroxyl substituent, wherein the heterocyclic group optionally further contains one or more heteroatoms； Z is an amino acid residue, &mdash；NR3R4, &mdash；NR5COR6, &mdash；NR5C(O)OR6； &mdash；NR5SOR6, NR5SO2R6； &mdash；NR5C(S)NR6R7, &mdash；NR5C(NR8)NR6R7, or &mdash；N&boxH；R9, where R3, R4, R5, R6, R7, R8 and R9 are independently hydrogen, or a group, optionally substituted, selected from alkyl, heteroalkyl, aryl, heteroaryl, aralkyl and heteroaralkyl, with the proviso that R9 is not hydrogen； and Y is &mdash；S&mdash； or &mdash；S(O)&mdash；. The compounds find use in the treatment of microbial infections.
