"Slim" nucleosides and nucleotides. I. Synthetic, structural and biophysical investigations of showdomycins

Kinetics of formation of GlcNAc-GlcNAc-P-P-dolichol by microsomes from the retina of the embryonic chick

Little quantitative information is available concerning individual reactions of the dolichol pathway. We have investigated the kinetics of the GlcNAc-transferase that catalyzes the biosynthesis of GlcNAc-GlcNAc-P-P-dolichol using chemically synthesized GlcNAc-P-P-dolichol as the substrate. Using microsomal preparations from the retina of the embryonic chick as enzyme source, optimal incubation conditions of pH, metal ion and detergent concentrations were established, after which apparent kinetic constants (Km and Vmax) were determined under initial rate conditions for GlcNAc-P-P-dolichol and UDP-GlcNAc. These studies provide the first quantitative description of the kinetics of this reaction.

The Elusive Antiaromaticity of Maleimides and Maleic Anhydride: Enthalpies of Formation of N-Methylmaleimide, N-Methylsuccinimide, N-Methylphthalimide, and N-Benzoyl-N-methylbenzamide

In order to understand the antiaromaticity of maleimides, the enthalpies of formation and sublimation of N-methylmaleimide, N-methylsuccinimide, N-methylphthalimide, and N-benzoyl-N-methylbenzamide were measured. The numerical values of enthalpies of formation for these compounds in the solid state are -329.3 +/- 1.4, -469.8 +/- 1.6, -325.0 +/- 2.1, and -239.6 +/- 3.8 kJ mol(-)(1), respectively, while the corresponding values in the gaseous state are -256.0 +/- 1.5, -389.7 +/- 1.6, -233.9 +/- 2.2, and -119.5 +/- 3.8 kJ mol(-)(1), respectively. The values of enthalpies of sublimation for the same compounds are 73.3 +/- 0.5, 80.1 +/- 0.3, 91.1 +/- 0.5, and 120.1 +/- 0.4 kJ mol(-)(1), respectively. We find that the antiaromaticity of maleimides is only modest.