Novel open-chain and cyclic conformationally constrained (R)- and (S)-α,α-disubstituted tyrosine analogues

Article abstract of DOI:10.1002/hlca.19950780613

A series of novel open-chain and cyclic conformationally constrained (R)- and (S)-α,α-disubstituted tyrosine analogues 1a-e were synthesized in good yields and high optical purities. The absolute configurations of these tyrosine analogues were unambiguously determined based on the X-ray structures of the precursor diastereoisomeric peptides of type 4 and 5. Four of these structures are deseribed, showing β-turn type-I geometries for dipeptides 4b, 5b, and 4c and an extended conformation for peptide 5c. The conversion of the free amino acids 1a-c into suitably protected building blocks 11a-d and 15d,e for peptide synthesis is discussed.