P. C. Srivastava

Synthesis of arylboronic acids via the reaction of borane with arylmagnesium halides

Abstract The reaction of borane complexes with arylmagnesium halides produces the corresponding arylborohydrides in high yield. The arylborohydrides are readily hydrolyzed to the arylboronic acids. The syntheses are conveniently carried out in one pot. The reaction mechanism was clarified via a boron-11 NMR study.

Synthesis and Properties of Purine Nucleosides and Nucleotides

Inosinic acid was the first nucleotide obtained from nature and was reported by von Liebig in 1847. This was followed by the isolation of the first nucleoside, guanosine, by E. Schulze and E. Brosshard in 1885. Subsequently, other naturally occurring purine nucleosides and nucleotides were isolated and characterized as the degradation products of ribonucleic acids (RNAs) and deoxyribonucleic acids (DNAs). The biochemical significance of nucleosides and nucleotides became more apparent in the early 1950s when the era of modern molecular biology was introduced by the classical work of J. D. Watson and F. H. C. Crick on the structure of DNA in 1953 and by the great discovery of the “second messenger” of hormone action, adenosine cyclic 3′,5′-(hydrogen)phosphate (cyclic AMP or cAMP) by Earl W. Sutherland in 1957. The synthesis of nucleosides and nucleotides then became instrumental in identifying the naturally occurring nucleosides and their metabolites and in an understanding of the biochemical and enzymatic reactions and pathways. Discoveries made in the field of purine nucleoside and nucleotide chemistry have contributed substantially to a better understanding of biology at the molecular level, which reached a pinnacle with the decoding of the genetic code and ultimate synthesis of the chemical gene by H. G. Khorana.

Synthesis of Vinyl Bromides Via Reaction of Vinyl Boronic Acids with Sodium Bromide

Abstract Vinyl halides have proven to be useful synthetic intermediates.1,2 Recently, it was discovered that vinyl iodides are more stable to in-vivo deiodination than the corresponding alkyl iodides.3,4 This fact makes the vinyl halides potentially valuable in the design and syntheses of radiopharmaceuticals. Because of our interest in pharmaceutical design, we recently developed a synthesis of vinyl iodides in which vinyl boronic acids are allowed to react with sodium iodide in the presence of mild oxidizing agents.5 The method has been successfully applied to a variety of functionally substituted, physiologically active molecules including fatty acids and steroids.6 We now wish to report that vinyl bromides are readily synthesized via the reaction of vinyl boronic acids with sodium bromide in the presence of mild oxidizing agents such as N-chlorosuccinimide.

An Unusual Iodine Monochloride Chlorination of an Imidazole Nucleoside

Abstract The reaction of iodine monochloride with the imidazole nucleoside, 5-amino-1-(2,3,5-tri-0-acetyl-α-D-ribofuranosyl)imidazole-4-carboxamide, provides the 2-chloroimidazole nucleoside in good yield.

Faciie-Radioiododemetallation Reactions for the Convenient Preparation of Raoioiodinated Compounds

Abstract Several new methods for the preparation of vinyl iodides via mercuration and thallation reactions of vinylboronic acids have been explored. Chloramine-T oxidation of alkylvinylmercury iodides or iodide treatment of alkylvinylthallium trifluoroacetate substrates, prepared from the corresponding alkylvinylboronic acid and thallic trifluoroacetate, yields the corresponding alkylvinyl iodides. These method are also efficient for the synthesis of the corresponding radioiodinated compounds.

NEW RADIOHALOGENATED ALKENYL TELLURIUM FATTY ACIDS

Abstract Radiolabeled long-chain fatty acids have diagnostic value as radiopharmaceutical tools in myocardial imaging. Some applications of these fatty acids are limited due to their natural metabolic degradation in vivo with subsequent washout of the radioactivity from the myocardium. The identification of structural features which will increase the myocardial residence time without decreasing the heart uptake of long-chain fatty acids is of interest. Fatty acids containing the tellurium heteroatom were the first modified fatty acids developed and show unique prolonged myocardial retention and low blood levels. Our detailed studies with radioiodinated vinyliodide substituted tellurium fatty acids demonstrate that heart uptake is a function of the tellurium position. New techniques of tellurium and organoborane chemistry have been developed for the synthesis of a variety of radioiodinated iodoalkenyl tellurium fatty acids.

The Synthesis of 2-Nitro-1-[(2-Hydroxyethoxy)Methyl]Imidazole (Azomycin Acyclonucleoside)

Synthesis of acyclonucleosides as analogues of naturally occurring ribonucleosides has been the subject of major research investigations since the advent of the chemotherapeutic agent acyclovir (Zovirax), an acyclic analogue of guanosine. The intensity of research interest in this area is obvious from the fact that almost every conceivable acyclic analogue of naturally occurring or biologically active synthetic nucleosides have been prepared during the past decade. The synthesis of 2-nitro-1-((2-hydroxyethoxy)methyl)imidazole, the acyclonucleoside analogue of antibiotic azomycin (azomycin acyclonucleoside), is accomplished via alkylation of azomycin with 2-benzoyloxyethoxymethylene chloride followed by debenzoylation.