Naeema Khan

Cis-Diastereoselectivity in Pictet–Spengler Reactions of L-Tryptophan and Electronic Circular Dichroism Studies

The diastereoselective synthesis of optically active 1,3-disubstituted tetrahydro-β-carbolines using polar protic Pictet-Spengler cyclization of (S)-tryptophan methyl ester with five aldehydes RCHO (R═CH(3), C(2)H(5), C(3)H(7), C(4)H(9), and C(6)H(5)) was studied. As an alternate route, the cyclization of (S)-tryptophan with the same aldehydes and subsequent methylation of the resulting tetrahydro-β-carboline carboxylic acids were also performed for comparison. (13)C NMR and electronic circular dichroism (ECD) studies and time-dependent density functional theory ECD calculations data established the relative 1,3 cis/trans and the absolute configuration (1S,3S/ 1R,3S) of the synthesized compounds. The solid-state and solution ECD study of the prepared compounds, supported by ECD calculation and X-ray data, afforded a reliable ECD method for the configurational assignment of 1,3-disubstituted tetrahydro-β-carbolines and revealed the stereochemical factors that determine the characteristic ECD data.

Methyl 2-(2-hydroxyacetamido)benzoate

The title compound, C10H11NO4, was formed from 4,1-benzoxazepine-2,5(1H,3H)-dione and ammonia gas. Intramolecular hydrogen bonding is present between the amide N—H group and the carbonyl O atom of the ester group. The crystal structure features intermolecular O—H⋯O hydrogen bonds.

Synthesis, Characterization and Investigation of Side Chain Length and/or Substituents Effect on the Liquid Crystal Properties of New Mesogens

New substituted and unsubstituted phenol based mesogene series having an azo central linkage was synthesized by fixing phenol as rigid core unit with aromatic amine. The terminal –OH group was esterified successively by long alkyl chain acid chloride of variable length (n=2, 6, 11, 15, 17). All 25 synthesized compounds exhibit mesomorphism. The effect of side chain length and substituents on the stability of liquid crystals was studied. The study reveals that nitro substituent destabilizes nematic and smectic phases more than floro substituent. Furthermore, the transition temperature decreases as the length of side chain increases.

cis-(9S,10S)-Methyl 1-propyl-1,2,3,4-tetra-hydro-β-carboline-3-carboxyl-ate.

The title compound, C16H20N2O2, was synthesized from (S)-tryptophan methyl ester hydrochloride and butyraldehyde. The absolute configuration 9S,10S was assigned on the basis of the unchanging chirality of the C9 centre. The NH group of the indole ring is involved in intermolecular N—H⋯O hydrogen bonding, while the NH group of the six-membered ring is not. This latter ring has a half-chair conformation.

3-Chloro-N′-hydr­oxy-N-(1-naphth­yl)benzene­carboximidamide

The molecule of the title compound, C17H13ClN2O, adopts a cis configuration with respect to the C=N bond. The crystal structure features O-H center dot center dot center dot N hydrogen bonding.