Patent ID: 8258329

Claim:
A compound of the formula: wherein: R 1 and R 2 are each independently: alkyl (C≦12) , alkenyl (C≦12) , or a substituted version of either of these groups; or R 1 and R 2 are taken together and are alkanediyl (C≦12) or alkenediyl (C≦12) ; and R 20 , R 21 , and R 22 are each independently: hydrogen, hydroxy, halo, oxo, or amino; or alkyl (C≦12) , alkenyl (C≦12) , alkoxy (C≦12) , acyl-oxy (C≦12) , alkylsilyl-oxy (C≦12) , or a substituted version of any of these groups; or a pharmaceutically acceptable salt, tautomer, acetal, or ketal thereof.