A compound of the formula I or II or a pharmaceutically acceptable salt thereof for use as a medicament as an antimicrobial agent: wherein: X is O, S or SO 2, Y is OH or C 1 to C 10 alkyl, R 1, R 2 and R 4 are each independently selected from H and C 1 to C 6 alkyl, R 3 is selected from a functional group selected from H, C 1 to C 6 alkyl, and a carbonyl-containing group, R 12 is: a substituent selected from H, alkenyl, "aryl", trihaloalkyl and C 1 to C 6 alkyl, wherein the "aryl" group is a monocyclic or polycyclic aromatic hydrocarbyl group having at least 5 carbon atoms, or comprises a monocyclic or polycyclic aromatic hydrocarbyl group having at least 5 carbon atoms and a linking group of the formula -[CR 14 R 15] t that is coupled to the cyclic or polycyclic aromatic ring, wherein R 14 and R 15 are each independently selected from H or C 1 or C 2 alkyl and t is an integer of 0 to 12, and wherein substitution takes place via the linking group; and wherein, where R 12 is alkenyl or "aryl", the alkenyl or "aryl" group is optionally substituted with one or more of halo, nitro, ether and t-butyldimethylsilylether (TBDMSO). R 5 and R 7 are each a group of the formula L 1 -L 2 -R 6 or L 2 -L 1 -R 6, where L 1 is a linker of the formula -[CR 8 R 9] n -, where n is an integer of from 0 to 12, and R 8 and R 9 are each independently selected from H or C 1 to C 2 alkyl, and where L 2 is absent or a linker that is selected from O, S, SO, SO 2, N(R'), C, C O, OC, [O(CR' 2) r] s, [(CR' 2) r O] s CH(OR'), C N(R'), N(R')C, N(R')C N(R'), SO 2 N(R') or N(R')SO 2 where R' and R" are each independently selected from hydrogen and a C 1 to C 2 alkyl, and where r is 1 or 2 and s is 1 to 4, and where R 6 is selected from OR 13, heterocyclic and C 1 to C 25 hydrocarbyl group, wherein R 13 is a C 1 to C 6 alkyl, and said heterocyclic and hydrocarbyl group is optionally substituted with at least one functional group selected from alkenyl, alkyl, aryl, halo, trihaloalkyl, alcohol, keto, S R 13, sulfonyl, thio-alcohol, ester, thioester, ether, thioether, amide, thioamide, urea, thiourea, =O, =S, amine and heterocyclic group, and wherein alkyl is defined as cyclic and non-cyclic alkyl. X is O, S or SO 2, Y is OH or C 1 to C 10 alkyl, R 1, R 2 and R 4 are each independently selected from H and C 1 to C 6 alkyl, R 3 is selected from a functional group selected from H, C 1 to C 6 alkyl, and a carbonyl-containing group, R 12 is: a substituent selected from H, alkenyl, "aryl", trihaloalkyl and C 1 to C 6 alkyl, wherein the "aryl" group is a monocyclic or polycyclic aromatic hydrocarbyl group having at least 5 carbon atoms, or comprises a monocyclic or polycyclic aromatic hydrocarbyl group having at least 5 carbon atoms and a linking group of the formula -[CR 14 R 15] t that is coupled to the cyclic or polycyclic aromatic ring, wherein R 14 and R 15 are each independently selected from H or C 1 or C 2 alkyl and t is an integer of 0 to 12, and wherein substitution takes place via the linking group; and wherein, where R 12 is alkenyl or "aryl", the alkenyl or "aryl" group is optionally substituted with one or more of halo, nitro, ether and t-butyldimethylsilylether (TBDMSO). R 5 and R 7 are each a group of the formula L 1 -L 2 -R 6 or L 2 -L 1 -R 6, where L 1 is a linker of the formula -[CR 8 R 9] n -, where n is an integer of from 0 to 12, and R 8 and R 9 are each independently selected from H or C 1 to C 2 alkyl, and where L 2 is absent or a linker that is selected from O, S, SO, SO 2, N(R'), C, C O, OC, [O(CR' 2) r] s, [(CR' 2) r O] s CH(OR'), C N(R'), N(R')C, N(R')C N(R'), SO 2 N(R') or N(R')SO 2 where R' and R" are each independently selected from hydrogen and a C 1 to C 2 alkyl, and where r is 1 or 2 and s is 1 to 4, and where R 6 is selected from OR 13, heterocyclic and C 1 to C 25 hydrocarbyl group, wherein R 13 is a C 1 to C 6 alkyl, and said heterocyclic and hydrocarbyl group is optionally substituted with at least one functional group selected from alkenyl, alkyl, aryl, halo, trihaloalkyl, alcohol, keto, S R 13, sulfonyl, thio-alcohol, ester, thioester, ether, thioether, amide, thioamide, urea, thiourea, =O, =S, amine and heterocyclic group, and wherein alkyl is defined as cyclic and non-cyclic alkyl.