Patent ID: 8338618

Claim:
A compound of the formula: wherein: R a is azido, fluoro, hydroxyamino, alkoxyamino (C≦12) , substituted alkoxyamino (C≦12) , or —NH-L-R d ; wherein: L is alkanediyl (C≦8) ; and R d is: hydroxy; or alkoxy (C≦18) , aryloxy (C≦18) , or acyloxy (C≦18) , or a substituted version of any of these groups; R 1 is: hydrogen, cyano, hydroxy, halo or amino; or alkyl (C≦8) , alkenyl (C≦8) , alkynyl (C≦8) , aryl (C≦8) , aralkyl (C≦8) , heteroaryl (C≦8) , heteroaralkyl (C≦8) , acyl (C≦8) , alkoxy (C≦8) , aryloxy (C≦8) , acyloxy (C≦8) , alkylamino (C≦8) , arylamino (C≦8) , amido (C≦8) , or a substituted version of any of these groups; R 4 and R 5 are each independently alkyl (C≦18) or substituted alkyl (C≦18) ; R 6 is hydrogen, hydroxy or oxo; and or a pharmaceutically acceptable salt, tautomer, or optical isomer thereof.