Patent ID: 8012975

Claim:
A compound of the following formula or a pharmaceutically acceptable salt thereof: wherein: R 1 is —CH 2 —N(R a ) 2 or —CH 2 —OR a , where R a is H; alkyl-CO—; haloalkyl-CO—; cycloalkylalkyl-CO—; haloalkyl-O—CO—; arylalkyl-CO—; arylalkenyl-CO—; heteroaryl-CO—; alkenyl-CO—; alkenyl; amino acid acyl; or a protecting group; R 5 is OR″, where R″ is H; alkyl-CO—; cycloalkyl-CO—; haloalkyl-CO—; or a protecting group; R 18 is —OR, where R is H; alkyl-CO—; cycloalkylalkyl-CO—; or a protecting group; and R 21 is —OH; provided that where an amino group is protected, the amino group together with the protecting group forms: (a) a carbamate selected from the group consisting of alkyl, arylalkyl, sulpho- or halo-arylalkyl, alkylsilylalkyl, arylalkyl, cycloalkylalkyl, alkylarylalkyl, heterocyclylalkyl, nitroarylalkyl, acylaminoalkyl, nitroaryldithioarylalkyl, dicycloalkylcarboxamidoalkyl, cycloalkyl, alkenyl, arylalkenyl, nitroarylalkenyl, heterocyclylalkenyl, heterocyclyl, hydroxyheterocyclyl, alkyldithio, alkoxy- or halo- or alkylsulphinyl arylalkyl, and heterocyclylacyl carbamate; (b) an aroyl, arylaroyl, haloaroyl, or nitroaroyl amide; or (c) alkylamino, alkylsilylalkoxyalkylamino, alkoxyalkylamino, cyanoalkylamino, heterocyclylamino, alkoxyarylalkylamino, cycloalkylamino, nitroarylamino, arylalkylamino, or alkoxy- or hydroxy-arylalkylamino; and where a hydroxy group is protected, the hydroxyl group together with the protecting group forms: (a) an ether selected from the group consisting of alkyl, alkoxyalkyl, aryloxyalkyl, alkoxyalkoxyalkyl, alkylsilylalkoxyalkyl, alkylthioalkyl, arylthioalkyl, azidoalkyl, cyanoalkyl, chloroalkyl, heterocyclic, cycloalkylalkyl, alkenyl, cycloalkyl, alkylarylalkyl, alkoxyarylalkyl, nitroarylalkyl, haloarylalkyl, alkylaminocarbonylarylalkyl, alkylsulfinylarylalkyl and alkylsilyl ether; or (b) arylacyloxy, aryl alkyl carbonate, aliphatic carbonate, alkylsulfinylarylalkyl carbonate, alkyl carbonate, aryl haloalkyl carbonate, aryl alkenyl carbonate, arylcarbamate, alkylphosphinyl, alkylphosphinothioyl, arylphosphinothioyl, or alkyl sulphonate.