A pharmaceutical composition comprising a phamaceurtical diluent and a compound of formula IV wherein R21= H, C1-C20 alkyl, cycloalkyl, alkenyl, aryl, arylalkyl, or alkylaryl, -CH2OR25, -C(O)R25, -CO(O)R25, -C(O)NR25R26, -CH2C(O)R25, or ûCH2C(O)NHR25, where R25 and R26 are each independently H, C1-C
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