Collections of compounds

A compound of formula II:

• wherein R2 and R3 are independently selected from:
• H, R, OH, OR, ═O, ═CH—R, ═CH2, CH2—CO2 R , CH2—CO2H, CH2-SO2R, O—SO2R, CO2R, COR and CN, and there is optionally a double bond between C1 and C2 or C2 and C3;
• R6, R7, R8 and R9 are independently selected from H, R, OH, OR, halo, nitro, amino, Me3Sn;
• or R7 and R8 together form a group —O—(CH2)p—O—, where p is 1 or 2;
• where R is a lower alkyl group having 1 to 10 carbon atoms, or an aralkyl group of up to 12 carbon atoms, whereof the alkyl group optionally contains one or more carbon—carbon double or triple bonds, which may form part of a conjugated system, or an aryl group of up to 12 carbon atoms;
• and is optionally substituted by one or more halo, hydroxy, amino, or nitro groups, and optionally contains one or more hetero atoms, which may form part of, or be, a functional group;
• except that
• one or more of R6, R7, and R8 are independently X—Y—A—, where X is selected from —COZ′, NHZ, SH, or OH, where Z is either H or a nitrogen protecting group, Z′ is either OH or an acid protecting group, Y is a divalent group such that HY=R, and A is O.