title: Conformation and crystal structures of 1-amino-cyclo-hexa-neacetic acid (β(3,3)Ac6c) in N-protected derivatives.
abstract: N-Protected derivatives of 1-amino-cyclo-hexa-neacetic acid (β(3,3)-Ac6c), namely Valeroyl-β(3,3)-Ac6c-OH [2-(1-pentanamidocyclohexyl)acetic acid, C13H23NO3], (I), Fmoc-β(3,3)-Ac6c-OH [2-(1-{[(9H-fluoren-9-yloxy)carbonyl]amino}cyclohexyl)acetic acid, C23H25NO4], (II), and Pyr-β(3,3)-Ac6c-OH {2-[1-(pyrazine-2-amido)cyclohexyl]acetic acid, C13H17N3O3}, (III), were synthesized and their conformational properties were determined by X-ray diffraction analysis. The backbone torsion angles (ϕ, θ) for β(3,3)-Ac6c-OH are restricted to gauche conformations in all the derivatives, with a chair conformation of the cyclo-hexane ring. In the crystal structure of (I), the packing of mol-ecules shows both carb-oxy-lic acid R 2 (2)(8) O-H⋯O and centrosymmetric R (2) 2(14) N-H⋯O hydrogen-bonding inter-actions, giving rise to chains along the c-axis direction. In (II), centrosymmetric carb-oxy-lic acid R 2 (2)(8) O-H⋯O dimers are extended through N-H⋯O hydrogen bonds and together with inter-ring π-π inter-actions between Fmoc groups [ring centroid distance = 3.786 (2) Å], generate a layered structure lying parallel to (010). In the case of compound (III), carb-oxy-lic acid O-H⋯Npyrazine hydrogen bonds give rise to zigzag ribbon structures extending along the c-axis direction.
authors.affiliation: Medicinal Chemistry Division, Indian Institute of Integrative Medicine, Canal Road, Jammu Tawi 180 001, India.
authors.forename: Naiem
authors.initials: N
authors.lastname: Ahmad Wani
authors.affiliation: X-ray Crystallography Laboratory, Post-Graduate Department of Physics & Electronics, University of Jammu, Jammu Tawi 180 006, India.
authors.forename: Vivek K
authors.initials: VK
authors.lastname: Gupta
authors.affiliation: X-ray Crystallography Laboratory, Post-Graduate Department of Physics & Electronics, University of Jammu, Jammu Tawi 180 006, India.
authors.forename: Rajni
authors.initials: R
authors.lastname: Kant
authors.affiliation: Medicinal Chemistry Division, Indian Institute of Integrative Medicine, Canal Road, Jammu Tawi 180 001, India.
authors.forename: Subrayashastry
authors.initials: S
authors.lastname: Aravinda
authors.affiliation: Medicinal Chemistry Division, Indian Institute of Integrative Medicine, Canal Road, Jammu Tawi 180 001, India.
authors.forename: Rajkishor
authors.initials: R
authors.lastname: Rai
keywords: conformation; crystal structure; disubstituted-β-amino acids; hydrogen bonds; π–π inter­action