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

✍ Scribed by K. Suguna; S. Ramakumar; N. Shamala; B. V. Venkataram Prasad; P. Balaram

• Publisher: Wiley (John Wiley & Sons)
• Year: 1982
• Tongue: English
• Weight: 340 KB
• Volume: 21
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360210912

✦ Synopsis

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 P2~1~2~1~2~1~ 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 C^α^ 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 C^α^ and Ile C^α^ 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.