τ-Regioselective addition of (-)-Nα-tert-butoxycarbonyl-L-histidine methyl ester to diethyl fumarate

Abstract

Dedicated to Professor Enrique AbstractAddition of (-)-N α -tert-butoxycarbonyl-L-histidine methyl ester to diethyl fumarate regioselectively yielded diethyl 2-[4-(2-methoxycarbonyl-2-tert-butoxycarbonylaminoethyl) imidazol-1-yl] succinate as a 1:1 mixture of diastereomers. These compounds were identified by NMR using Eu(fod) 3 as a stereospecific shift reagent, but were impossible to separate and characterise independently. Neutral hydrolysis of the mixture yielded the corresponding deprotected diastereomeric N τ -(2-ethoxycarbonyl-1-carboxy)ethyl-L-histidine..

Development of a Regioselective N-Methylation of (Benz)imidazoles Providing the More Sterically Hindered Isomer

“…(NH)-(Benz)imidazoles used in the regioselective methylation were either commercially available or prepared according to a reported procedure: (E)-methyl 3-(1H-imidazol-5-yl)acrylate, 16 (S)-methyl 2-((tert-butoxycarbonyl)amino)-3-(1H-imidazol-4-yl)propanoate, 17 4,5methyl-phenylimidazole, 4-(p-substituted-aryl)imidazoles, 18 5-(2-fluorophenyl)-1H-imidazole, 19 and benzimidazoles. 20 General Procedure for Protection of 4-Methyl-1H-imidazole.…”

Novel Generation of pH Indicators for Proton Magnetic Resonance Spectroscopic Imaging

“…Moreover, IEPA became rapidly removed from the circulation by renal clearance, a circumstance that imposed very high delivery doses to compensate its elimination. To overcome some of these drawbacks, we recently described a new pH probe derived from L-histidine 1 10 to increase the polar nature of the molecule and increase its retention time within the circulation (Chart 1). However, its apparent pK a ′ ) 5.58 remained far from the physiological range, a circumstance that precluded further developments as a pH e indicator.…”