A compound of formula (IV): O is a solid support; L is a linking group or a single bond; X' is selected from CO, NH, S, or O; A is O, S, NH, or a single bond; R.sub.2 and R.sub.3 are independently selected from: H, R, OH, OR, .dbd.O, .dbd.CH--R, .dbd.CH.sub.2, CH.sub.2--CO.sub.2R, CH.sub.2--CO.sub.2H, CH.sub.2--SO.sub.2R, O--SO.sub.2R, CO.sub.2R, COR, CN and there is optionally a double bond between C1 and C2 or C2 and C3; R.sub.6, R.sub.7, and R.sub.9 are independently selected from H, R, OH, OR, halo, nitro, amino, Me.sub.3Sn; R.sub.11 is either H or R; Q is S, O or NH; R.sub.10 is a nitrogen protecting group; and Y is a divalent group such that HY.dbd.R, and other related compounds and collections of compounds. ##STR00001##