Temperature Nuclear Magnetic Resonance Spectroscopy Research Articles

Solvation State of Nicotinamide in Binary Solvents by 13C NMR Probing at Different Temperatures

Solvation state of pyridine-3-carboxamide (nicotinamide) was studied by means of different temperature nuclear magnetic resonance spectroscopy at different compositions of water–dimethyl sulfoxide solvent. The breaking of hydrogen bonds between heteronitrogen and water molecules takes place at X DMSO ~ 0.2–0.3 m.f. Changes in carboxamide substituent solvation consisting in the disappearance of water molecules occur at X DMSO ~ 0.4 m.f. The quantum chemical modeling of some nicotinamide solvates was performed along with NBO analysis and chemical shift calculations.

Utilization of an intramolecular hydrogen bond to increase the CNS penetration of an NK(1) receptor antagonist.

This paper describes the synthesis and physical and biological effects of introducing different substituents at the alpha-position of the tryptophan containing neurokinin-1 receptor antagonist [(R)-2-(1H-indol-3-yl)-1-methyl-1-((S)-1-phenyl-ethylcarbamoyl)-ethyl]-carbamic acid benzofuran-2-ylmethyl ester (CI 1021). The described compounds all exhibit less than 5 nM binding affinities for the human neurokinin-1 receptor and selectivity over the tachykinin NK(2) and NK(3) receptor subtypes. Application of variable temperature nuclear magnetic resonance spectroscopy studies of the amide and urethane protons was utilized to determine the existence of an intramolecular hydrogen bond. This intramolecular hydrogen bond increases the apparent lipophilicity to allow increased central nervous system penetration and pharmacological activity (gerbil foot tap test) in the case of the highest affinity compound [(S)-1-dimethylaminomethyl-2-(1H-indol-3-yl)-1-((S)-1-phenyl-ethylcarbamoyl)-ethyl]-carbamic acid benzofuran-2-ylmethyl ester (PD 174424) over those analogues that could not form an intramolecular hydrogen bond.

THE PHOTOOXIDATION OF 8‐METHOXYPSORALEN

Abstract— The photooxidation of 8‐methoxypsoralen has been studied. Enhancement of the reaction rate in deuterated solvents is in accord with the involvement of singlet oxygen. Several photoproducts including 6‐formyl‐7‐hydroxy‐8‐methoxycoumarin and polymer are formed. Low temperature nuclear magnetic resonance spectroscopy studies give evidence of a peroxidic intermediate.

CYCLOPHANES VI. TEMPERATURE DEPENDENT CONFORMATIONS OF 3,6-DIKETO[8](1,4)NAPHTHALENEOPHANE AND 3,6-DIKETO[8] (2,5)FURANOPHANE

Abstract A temperature dependent conformational change in the aliphatic chain of 3,6-diketo[8]naphthalenophane is observed by variable temperature nuclear magnetic resonance spectroscopy; the energy of activation for the process is 9.4±0.2 Kcal/mole. For 3,6-diketo[8](2,5)furanophane the conformational change of the chain is more facile than that of the ring with a conservative upper limit for ring rotation of about 9.1 Kcal/mole.

Addition reactions of heterocyclic compounds. Part LIV. Rotational isomerism of 6-aralkyl-5-oxidovinylphenanthridiniums: an investigation by variable temperature nuclear magnetic resonance spectroscopy

5-Oxidovinylphenanthridiniums with 6-aryl substituents exhibit cis–trans and rotational isomerism. The nature of the species involved has been elucidated by variable temperature n.m.r. spectroscopy and by observation of the properties of related compounds.

Addition reactions of heterocyclic compounds. Part XLIII. Rotational isomerism of 5-oxidovinylphenanthridiniums: an investigation by variable temperature nuclear magnetic resonance spectroscopy

5-Oxidovinylphenanthridiniums with 6-aryl substituents exhibit cis–trans and rotational isomerism. The nature of the species involved has been elucidated by variable temperature n.m.r. spectroscopy and by observation of the properties of related compounds.

A variable temperature nuclear magnetic resonance spectroscopy study of nitrogen inversion in medium-ring monocyclic and bicyclic systems

Nitrogen inversion barriers and structural effects on the barriers have been studied by variable temperature n.m.r. spectroscopy in monocyclic (six- and seven-membered ring) and bicyclic (bicyclo[2,2,2]octane and bicyclo[3,2,2]nonane) amines.