Cyclic dipeptides as building blocks for combinatorial libraries. Part 2: Synthesis of bifunctional diketopiperazines

Twenty-four bifunctional diketopiperazines, cyclo(-Aax-Bbx-) consisting of glutamic or aspartic acid (Aax) and lysine, ornithine or diaminobutyric (Dab) acid (Bbx) were synthesized. D-Dab moiety was incorporated as D-Gln followed by Hoffman-type rearrangement induced by Phl[OC(O)CF3](2.) Cyclization conditions for the related linear dipeptide precursors allowing racemization to be kept at a minimum were determined. (C) 2002 Elsevier Science Ltd. All rights reserved.