Inhibitors of serine proteases

A compound of formula I:

• or a pharmaceutically acceptable salt thereof, wherein
• R1 is an optionally substituted aryl:
• R2 and R3 together form an oxo group;
• A is —O—, or —CH2 —;
• R 4 is —NH—CHR4x—C(O)—(CO)—N(R4z)R4W;
• R4W is hydrogen, optionally substituted aliphatic, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted heterocycloaliphatic, or optionally substituted cycloaliphatic;
• R4Xis hydrogen, optionally substituted aliphatic, optionally substituted heteroaryl, optionally substituted phenyl, optionally substituted cycloaliphatic, or optionally substituted heterocycloaliphatic;
• R4Z is hydrogen, optionally substituted aliphatic, optionally substituted cycloaliphatic, optionally substituted heterocycloaliphatic, optionally substituted aryl, or optionally substituted heteroaryl;
• R5 is
• R13 is
• T is —C(O)—, and
• R is