lfonyl, substituted or unsubstituted carbocyclic aryl, or a substituted or unsubstituted heteroaromatic or heteroalicyclic group having from 1 to 3 rings, 3 to 8 ring members in each ring and from 1 to 3 hetero atoms, with at least one of R and R1 being other than hydrogen; each R2 and each R3 are each independently hydrogen, halogen, hydroxyl, azido, substituted or unsubstituted alkyl, substitute