2Bz4OH5Piperaz-N-IndanBuCONH2 isostere 5-[2(S)-[(1,1-Dimethylethyl)aminocarbonyl]-1-piperazinyl]-4(S)-hydroxy-N-(2(R)-hydroxy-1(S)-indanyl)-2(R)-(phenylmethyl)pentanamide AIDS-006756 AIDS006756 L-735,524 analog