: N-[[6-[[(Diphenylmethoxy)carbonyl]amino]-9H-purin-9-yl]acetyl]-N-[2-[[(9H-fluoren-9-ylmethoxy)carbonyl]amino]ethyl]glycine, N-[2-[[[(9H-Fluoren-9-yl)methoxy]carbonyl]amino]ethyl]-N-[2-[6-[[(benzhydryloxy)carbonyl]amino]-9H-purin-9-yl]acetyl]glycine