Ten‐membered cyclotripeptides

Abstract
The crystal structure of a conformationally restricted cyclotripeptide containing N‐methylanthranilic acid, l‐phenylalanine and l‐proline has been determined. The 10‐membered ring of cyelo(‐MeAnt‐Phe‐Pro‐) is characterized by a pseudosymmetry plane and by three cis amide bonds. The MeAnt aromatic ring makes an angle of 63.3° with the best plane of the backbone and is nearly perpendicular to the plane of the two adjacent amide bonds. The proline ring adopts βαT twist conformation (Ps = 144°) and the benzylic side chain is extended towards the nitrogen. An analysis of i.r. and n.m.r. spectral data indicates that the solution conformation retains the features found in the crystals. Crystal data: orthorhombic, P212121 with a= 10.153(3), b= 11.700(3), c= 16.402(3) Å and Z = 4. The final R and Rw are 0.047 and 0.067, respectively.

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