Crystal structures of diketopiperazines containing α-aminoisobutyric acid: Cyclo(Aib-Aib) and cyclo(Aib-L-Ile)

Suguna, K. ; Ramakumar, S. ; Shamala, N. ; Prasad, B. V. Venkataram ; Balaram, P. (1982) Crystal structures of diketopiperazines containing α-aminoisobutyric acid: Cyclo(Aib-Aib) and cyclo(Aib-L-Ile) Biopolymers, 21 (9). pp. 1847-1855. ISSN 0006-3525

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Official URL: http://www3.interscience.wiley.com/journal/1075863...

Related URL: http://dx.doi.org/10.1002/bip.360210912

Abstract

The crystal and molecular structures of two α-aminoisobutyric acid (Aib)-containing diketopiperazines, cyclo(Aib-Aib) 1 and cyclo(Aib-L-Ile) 2, are reported. Cyclo(Aib-Aib) crystallizes in the space group P1 with a = 5.649(3), b = 5.865(2), c = 8.363(1), α= 69.89(6), β = 113.04(8), γ = 116.0(3), and Z = 1, while 2 occurs in the space group P212121 with a = 6.177(1), b = 10.791(1), c = 16.676(1), and Z = 4. The structures of 1 and 2 have been refined to final R factors of 0.085 and 0.086, respectively. In both structures the diketopiperazine ring shows small but significant deviation from planarity. A very flat chair conformation is adopted by 1, in which the Cα atoms are displaced by 0.07 Å on each side of the mean plane, passing through the other four atoms of the ring. Cyclo(Aib-Ile) favors a slight boat conformation, with Aib Cα and Ile Cα atoms displaced by 0.11 and 0.05 Å on the same side of the mean plane formed by the other ring atoms. Structural features in these two molecules are compared with other related diketopiperazines.

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Deposited On:18 Oct 2010 07:18
Last Modified:16 May 2016 15:15

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