wherein:

R¹ is an optionally substituted 4-, 5- or 6-membered heterocyclic ring having one or more heteroatoms, in which at least one carbon atom of the ring is substituted with O, N, or S;

X¹ is —CO— or —CS— or —CH₂CO— or CH(R⁴) wherein R⁴ is H or optionally substituted alkyl or —COOH or —COOR¹¹ wherein R¹¹ is optionally substituted alkyl;

X² and X³ are independently —CO— or —CS—;

Z is —CH₂— or —S— or —O— or —NH—;

Q is O or S;

R² is H or optionally substituted alkyl or an optionally substituted carbocyclic ring;

R³ is H or optionally substituted alkyl or an optionally substituted mono- or polycyclic ring, optionally having one or more heteroatoms in the ring(s) and optionally being a fused ring; or R² and R³ together form an optionally substituted mono- or polycyclic ring optionally having one or more heteroatoms in the ring(s) and optionally being a fused ring;

R⁵ and R⁶ are independently H, or lower alkyl;

R⁷ and R⁸ are independently H, or optionally substituted lower alkyl;

R⁹ and R¹⁰ are independently H, or optionally substituted alkyl, or an optionally substituted carbocyclic ring;

Y is —(CH₂)_n— where n is 0, 1, 2 or 3 provided that when R² and R³ form part of the ring n is 0;

provided that when R¹ is:

and X¹, X² and X³ are —CO—

and R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰ are H

and Z is —CH₂—

and Q is O

and Y is —(CH₂)_n— where n is 0,

then R² and R³ are not both H;