Patent ID: 7557099

Claim:
A compound of formula Ia or Ib: or a pharmaceutically acceptable salt thereof, wherein: the dotted lines indicate the optional presence of a double bond between C1 and C2 or C2 and C3; R 2 and R 3 are independently selected from —H, ═O, ═CH 2 , —CN, —R, OR, halo, ═CH—R, O—SO 2 —R, CO 2 R and COR; R 6 and R 9 are independently selected from H, R, OH, OR, SH, SR, NH 2 , NHR, NRR′, nitro, Me 3 Sn and halo; where R and R′ are independently selected from optionally substituted C 1-12 alkyl, heterocyclyl groups having 3 to 20 ring atoms of which 1 to 10 are heteroatoms independently selected from the group consisting of N, O and S and aryl or heteroaryl groups having 5 to 20 ring atoms, the heteroaryl groups having one or more heteroatoms independently selected from the group consisting of N, O and S, wherein the optional substituents are independently selected from halo, hydroxy, ether, alkoxy, acetal, hemiacetal, ketal, hemiketal, oxo, thione, imino, formyl, acyl, carboxy, thiocarboxy, thiolcarboxy, thionocarboxy, imidic acid, hydroxamic acid, ester, acyloxy, oxycaroyloxy, amino, amido, thioamido, acylamido, aminocaronyloxy, ureido, guanidino, tetrazolyl, amidino, nitro, nitroso, azido, cyano, isocyano, cyanato, isocyanato, thiocyano, isothiocyano, sulfhydryl, disulfide, sulfine, sulfonyl, sulfino, sulfo, sulfinate, sulfonate, sulfinyloxy, sulfonyloxy, sulfate, sulfamyl, sulfonamido, sulfamino, sulfonamino, sulfinamino, phosphino, phosphor, phosphinyl, phosphono, phosphonate, phosphonooxy, phosphate, phosphorous acid, phosphite, phosphoramidite, or phosphoramidate; R A is selected from H, R, OR, SH, SR, NH 2 , NHR, NRR′, nitro, Me 3 Sn and halo; R 10 is a carbamate-based nitrogen protecting group; and R 11 is an oxygen protecting group.