Cyclic side-chain-linked biphenyl ether tripeptide: H3N+-cyclo-[Phe(4-O)-Phe-Phe(3-O)]-OMe. Cl-

Article abstract of DOI:10.1107/S0108270196009262

The crystal structure of the chloride salt of H₃N⁺-cyclo-(Phe^(4-O)-Phe-Phe^(3-O))-OMe, cyclo-phenylalanyl-phenylalanyl-phenylalaninium chloride methyl esther, C₂₈H₃₀N₃O₅⁺·Cl^-, is described. It is oxidatively linked through a biaryl ether linkage formed from the hydroxyl of 4-hydroxyphenylalanine and the meta position of the distal phenylalanine residue. This is the first reported crystal-structure determination of a cyclic 17-membered biphenyl ether tripeptide, a class which includes the natural products K-13 and OF4949 I-IV. An unusual C-H...O hydrogen bond is formed between the methine H atom of the N-terminal Cα and a carbonyl-O atom of a neighboring molecule [C...O=2.995(4)A].