2,2-Dimethyl-succinic acid 4-((1R,3aS,5aR,5bR,7aR,9S,11aR,11bR,13aR,13bR)-3a-hydroxymethyl-1-isopropenyl-5a,5b,8,8,11a-pentamethyl-eicosahydro-cyclopenta[a]chrysen-9-yl) ester 3-O-acyl betulin derivative AIDS-179205 AIDS179205