The title dipeptide, 1-(tert-butoxycarbonyl-D-alanyl)-N-isopropyl-L-pipecolamide or Boc-D-Ala-L-Pip-NH(i)Pr (H-Pip-OH is pipecolic acid or piperidine-2-carboxylic acid), C(17)H(31)N(3)O(4), with a D-L heterochiral sequence, adopts a type II' beta-turn conformation, with all-trans amide functions, where the C-terminal amide NH group interacts with the Boc carbonyl O atom to form a classical i+3 --> i intramolecular hydrogen bond. The C(alpha) substituent takes an axial position [H(alpha) (Pip) equatorial] and the trans pipecolamide function is nearly planar.
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http://dx.doi.org/10.1107/s0108270102008715 | DOI Listing |
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