ABSTRACT
The structural characterization of 1H-pyrrolo[2, 3-b]pyridine-3-acetic acid (alternative name: 7-azaindole-3-acetic acid), C(9)H(8)N(2)O(2), reveals similar molecular geometry, i.e. with the side chain perpendicular to the 7-azaindole ring, to that of the natural plant growth hormone indole-3-acetic acid (auxin) and its alkylated and halogenated derivatives.
Subject(s)
Acetates/chemistry , Indoleacetic Acids/physiology , Plants/chemistry , Pyridines/chemistry , Crystallography, X-Ray , Hydrogen Bonding , Ligands , Models, Molecular , Molecular ConformationABSTRACT
As part of molecular recognition studies on the phytohormone indole-3-acetic acid (IAA) a series of alkylated IAAs has been examined. Phenyl-ring substitution (alkyl = methyl and ethyl) at positions 4-, 6- or 7- as well as pyrrole substitution at the 2-site resulted in the six compounds which are analyzed: 2-Me-IAA, 4-Me-IAA, 6-Me-IAA, 7-Me-IAA, 4-Et-IAA and 6-Et-IAA. The structure-activity relationships investigated include those between the geometrical parameters of the molecular structures determined by X-ray analysis, the growth-promoting activities in the Avena coleoptile straight-growth bioassay and relative lipophilicities calculated from retention times on a reversed-phase HPLC column and from R(F) values in reversed-phase TLC. Lipophilicities are correlated with the moments of inertia, average polarizability, molecular mass, and the van der Waals radii of the ring substituents. The influence of substitution on the electronic properties of the indole ring and its geometry is discussed on the basis of the UV and 1H NMR spectra.
Subject(s)
Indoleacetic Acids/chemistry , Plant Growth Regulators/chemistry , Avena/drug effects , Avena/growth & development , Chromatography, Thin Layer , Cotyledon/drug effects , Indoleacetic Acids/pharmacology , Magnetic Resonance Spectroscopy , Plant Growth Regulators/pharmacology , Spectrophotometry, Ultraviolet , Structure-Activity Relationship , X-Ray DiffractionABSTRACT
The conformational characteristics of a flexible totally protected C-terminal dipeptide fragment (Boc-Phe-Leu-OBzl) of enkephalin are studied using X-ray data, molecular modelling and data retrieved from the Cambridge Structural Database. The dipeptide crystallizes with seven conformers in the asymmetric unit. C(27)H(36)N(2)O(5), T = 133 K, monoclinic, P2(1), a = 13.706 (3), b = 22.800 (3), c = 30.674 (5) Å, beta = 97.15 (3) degrees, V = 9511 (3) Å(3), Z = 14, D(c) = 1.145 Mg m(-3). Six of the seven molecules exhibit folded conformations with hydrophobic groups disposed at the opposite side of the peptide backbone. The characteristic Phi(1) and Psi(1) angles of the Phe residue and Phi(2) of the Leu fragment are in the allowed region defined in the Ramachandran diagram. However, they do not belong to the family of the lowest energy conformations. In the crystal, molecules are interconnected via N-H.O hydrogen bonds of peptide groups forming an infinite sheet similar to a parallel beta-sheet. Molecular dynamics simulations performed in vacuo reproduce the conformers and rotamers detected in the solid state.
