Improved conditions for a direct and regioselective synthesis of 8-carboxyethyl-7-deazaguanine

As deazaguanines have a broad range of applications, from medicinal research to supramolecular assemblies, simple pathways to functionalizable versions of this heterocycle are of noted importance. The cyclization reaction leading to deazaguanines is known to also lead to a furano-isomer, exclusively in some cases. 8-Carboxyethyl-7-deazaguanine (1) had failed to form through the typical cyclization conditions and previously required a considerably more longwinded synthetic approach to form over the furo-isomer (2). We report herein a more direct, simplified approach to 1 by iterative modification of the cyclization reaction conditions, which resulted in a complete reversal of regiochemistry in favor of the desired deazaguanine.     

Can a large neutron excess help solve the baryon loading problem in gamma-Ray burst fireballs?

We point out that the baryon loading problem in gamma-ray burst (GRB) models can be ameliorated if a significant fraction of the baryons which inertially confine the fireball is converted to neutrons. A high neutron fraction can result in a reduced transfer of energy from relativistic light particles in the fireball to baryons. The energy needed to produce the required relativistic flow in the GRB is consequently reduced, in some cases by orders of magnitude. A high neutron-to-proton ratio has been calculated in neutron star-merger fireball environments. Significant neutron excess also could occur near compact objects with high neutrino fluxes.     

Acyl radical insertion for the direct formation of new seven-substituted pterin analogs

A variety of pterin molecules were synthesized via an under-utilized acyl radical insertion, using aldehydes and α-keto esters as the acyl source. These reactions gave complete regiospecificity for the 7-isomer, with reaction times ranging in minutes, often with instantaneous product precipitation. This approach led to the construction of new pterin analogs unaccessible via traditional Friedel-Crafts acylation. The compounds were characterized by NMR spectroscopy and high-resolution mass spectroscopy.