Antibacterial agents

A compound of formula I,

• or a pharmaceutically acceptable salt thereof,
• wherein
• X═NH
• Y═CO, CS, —C(═N═CN) or
• X and Y together form an alkene, or C3-C5 cycloalkyl;
• R1 is —COOH;
• R2 is an electron withdrawing group;
• R4 is an optionally substituted aryl, provided that the aryl is not simultaneously substituted with a sulfonamide and a urea or thiourea, further provided that the aryl is not solely substituted at the ortho-position relative to Y, and still further provided that the aryl is not substituted with a group selected from
• W1 is N or CH;
• R10 is C1-C4 alkyl, C1-C4 substituted alkyl, Het, substituted Het, aryl, or substituted aryl;
• and
• R15 is H, C1-C4 alkyl, C1-C4 substituted alkyl, Het, substituted Het, C4-C7 cycloalkyl.