Synthesis of guanosine and its derivatives from 5-amino-1-beta-D-ribofuranosyl-4-imidazolecarboxamide. III. Formation of a novel cycloimidazole nucleoside and its cleavage reactions.

A new cycloimidazole nucleoside, 5-(1 inch -benzamido-1 inch-hydroxymethylene) amino-2', 1 inch-anhydro-1-beta-D-ribofuranosyl-4-imidazolecarboxamide (III) was synthesized by reaction of 5-amino-1-beta-D-ribofuranosyl-4-imidazolecarboxamide (AICA-riboside) with benzoyl isothiocyanate followed by methylation with methyl iodide. The structure of III was elucidated on the basis of its nmr spectra and chemical reactions. Of special interest are reactions of III with various nucleophiles. For example, guanosine (IX) was obtained by amination of III wtih ammonia in 72% yield. Analogous reactions of III with methylamine and dimethylamine gave N2-methylguanosine (X) and N2-dimethylguanosine (XI), respectively. Refluxing of III in alkaline solution afforded xanthosine (VII). The probable mechanism of formation and facile ring-opening of III is also discussed.     

Screening of Microorganisms Producing 5-Amino-4-imidazole-carboxamide and D-Ribose from 5-Amino-4-imidazole-carboxamide-riboside

Rice has evolved metabolic and morphological adaptations to low-oxygen stress to grow in submerged paddy fields. To characterize the molecular components that mediate the response to hypoxia in rice, we identified low-oxygen stress early response genes by microarray analysis. Among the highly responsive genes, five genes, OsHREF1 to OsHREF5, shared strong homology. They encoded small proteins harboring two EF-hands, typical Ca²⁺-binding motifs. Homologous genes were found in many land plants, including SlHREF in tomato, which is also strongly induced by hypoxia. SlHREF induction was detected in both roots and shoots of tomato plants under hypoxia. With the exception of OsHREF5, OsHREF expression was unaffected by drought, salinity, cold, or osmotic stress. Fluorescent signals of green fluorescent protein-fused OsHREFs were detected in the cytosol and nucleus. Ruthenium red, an inhibitor of intracellular Ca²⁺ release, repressed induction of OsHREF1-4 under hypoxia. The HREFs may be related to the Ca²⁺ response to hypoxia.     

The synthesis and antiviral activity of 4-fluoro-1-beta-D-ribofuranosyl-1H-pyrazole-3-carboxamide

A novel fluoropyrazole ribonucleoside has been shown to have significant anti-influenza activity in vitro. The compound is compared and contrasted with the structurally-related compound ribavirin in attempts to identify factors having significant bearing on the mode of action of both compounds.     

Biotransformation of 1-beta-D-ribofuranosyl-4-methylthiopyrazolo(3,4-d)pyrimidine and its 5'-monophosphate

1-beta-D-Ribofuranosyl-4-methylthiopyrazolo(3,4-d)pyrimidine (I) has been converted into its 5'-monophosphate (III) by reacting with POCl3 in trialkyl phosphates or by phosphorylating 2',3'-O-ethoxymethylidene derivative of riboside (I) using 2-cyanoethyl phosphate in the presence of DCC and subsequent removal of blocking groups. Condensation of nucleotide (III) imidazolide with pyrophosphoric acid afforded corresponding 5'-triphosphate. Pools of natural NTPs and riboside (I) phosphates were monitored by HPLC after administering riboside (I), phosphate (III), or 4-methylthiopyrazolo(3,4-d)pyrimidine (II) into mice with leukemia L1210 or after incubating CaOv culture cells with these compounds. Treatment with riboside (I) or nucleotide (III) possessing antileukemic and cytotoxic activites led to much higher level of monophosphate (III), than treatment with biologically inactive base (II). ATP and GTP levels in CaOv cells incubated with (I) or (III) decreased by 60-70%, whereas (II) did not affect NTP pool. Bioactivation of nucleoside (I) into monophosphate (III) proceeds via direct phosphorylation by adenosine kinase. No tranformation of (II) into (I) or (III) occurs under these conditions.     

Synthesis of guanosine and its derivatives from 5-amino-1-beta-D-ribofuranosyl-e-imidazolecarboxamide. IV. A new route to guanosine via cyanamide derivative.

4-Cyanamido-5-imidazolecarboxamide (IV) was prepared by brief treatment of 5-(S-methylisothiocarbamoyl) amino-4-imidazolecarboxamide (V) with alkali. Compound VI was converted in an alkaline solution to either guanine (VII) or isoguanine (VIII), depending on the concentration of alkali. This procedure was applied to the synthesis of 2',3'-0-isopropylideneguanosine (XVI) from the riboside of 5-(N'-benzoyl-S-methylthiocarbamoyl) amino-4-imidazolecarboxamide (IX), PROviding a new route to XVI.     

Structural studies of lipid A from Pseudomonas aeruginosa PAO1: occurrence of 4-amino-4-deoxyarabinose.

Lipid A derived from Pseudomonas aeruginosa PAO1 contains a biphosphorylated 1-6-linked glucosamine disaccharide backbone. The reducing glucosamine has an unsubstituted glycosidically linked phosphate at C-1. The nonreducing glucosamine has an ester-bound phosphate at C-4' which is nonstoichiometrically substituted with 4-amino-4-deoxyarabinose. Induction of 4-amino-4-deoxyarabinose was dependent on cultural conditions. No pyrophosphate groups were detected. Acyloxyacyl diesters are formed by esterification of the amide-bound 3-hydroxydodecanoic acid with dodecanoic acid and 2-hydroxydodecanoic acids in an approximate molar ratio of 2:1. Dodecanoic and 3-hydroxydecanoic acids are esterified to positions C-3 and C-3' in the sugar backbone. All hydroxyl groups of the glucosamine disaccharide except C-4 and C-6' are substituted. Lipopolysaccharide chemical analyses measured glucose, rhamnose, heptose, galactosamine, alanine, phosphate, and glucosamine. The proposed lipid A structure differs from previous models. There are significant differences in acyloxyacyl diesters, and the proposed model includes an aminopentose substituent.     

The kinetic mechanism of the human bifunctional enzyme ATIC (5-amino-4-imidazolecarboxamide ribonucleotide transformylase/inosine 5'-monophosphate cyclohydrolase). A surprising lack of substrate channeling

5-Amino-4-imidazolecarboxamide ribonucleotide transformylase/IMP cyclohydrolase (ATIC) is a bifunctional protein possessing two enzymatic activities that sequentially catalyze the last two steps in the pathway for de novo synthesis of inosine 5'-monophosphate. This bifunctional enzyme is of particular interest because of its potential as a chemotherapeutic target. Furthermore, these two catalytic activities reside on the same protein throughout all of nature, raising the question of whether there is some kinetic advantage to the bifunctionality. Rapid chemical quench, stopped-flow absorbance, and steady-state kinetic techniques were used to elucidate the complete kinetic mechanism of human ATIC. The kinetic simulation program KINSIM was used to model the kinetic data obtained in this study. The detailed kinetic analysis, in combination with kinetic simulations, provided the following key features of the enzyme reaction pathway. 1) The rate-limiting step in the overall reaction (2.9 +/- 0.4 s(-1)) is likely the release of tetrahydrofolate from the formyltransferase active site or a conformational change associated with tetrahydrofolate release. 2) The rate of the reverse transformylase reaction (6.7 s(-1)) is approximately 2-3-fold faster than the forward rate (2.9 s(-1)), whereas the cyclohydrolase reaction is essentially unidirectional in the forward sense. The cyclohydrolase reaction thus draws the overall bifunctional reaction toward the production of inosine monophosphate. 3) There was no kinetic evidence of substrate channeling of the intermediate, the formylaminoimidazole carboxamide ribonucleotide, between the formyltransferase and the cyclohydrolase active sites.     

Inhibition of phytochrome synthesis by the transaminase inhibitor, 4-amino-5-fluoropentanoic Acid

Gardner and Gorton (1985 Plant Physiol 77: 540-543) demonstrated that the transaminase inhibitor gabaculine (5-amino-1,3-cyclohexadienyl-carboxylic acid) inhibits the initial synthesis and resynthesis of spectrophotometrically detectable phytochrome in vivo. Another mechanism-based transaminase inhibitor, 4-amino-5-fluoropentanoic acid (AFPA), is examined in this report for its effects on phytochrome synthesis in developing etiolated seedlings. Preemergence treatment with AFPA was found to inhibit initial phytochrome synthesis in peas (Pisum sativum L.), corn (Zea mays L.), and oats (Avena sativa L.). In general, reduction in phytochrome correlated with reduction in chlorophyll. However, the extent of inhibition of phytochrome synthesis was not as great as that of chlorophyll synthesis. These results confirm those with gabaculine, indicating that both initial synthesis and resynthesis of phytochrome require de novo synthesis of chromophore as well as apoprotein. AFPA was a more effective inhibitor of both chlorophyll and phytochrome synthesis than was gabaculine, suggesting that AFPA may be the preferred tool with which to probe the physiological consequences of the inhibition of phytochrome biosynthesis.     

A Salmonella typhimurium cobalamin-deficient mutant blocked in 1-amino-2-propanol synthesis.

Salmonella typhimurium synthesizes cobalamin (vitamin B12) when grown under anaerobic conditions. All but one of the biosynthetic genes (cob) are located in a single operon which includes genes required for the production of cobinamide and dimethylbenzimidazole, as well as the genes needed to form cobalamin from these precursors. We isolated strains carrying mutations (cobD) which are unlinked to any of the previously described B12 biosynthetic genes. Mutations in cobD are recessive and map at minute 14 of the linkage map, far from the major cluster of B12 genes at minute 41. The cobD mutants appear to be defective in the synthesis of 1-amino-2-propanol, because they can synthesize B12 when this compound is provided exogenously. Labeling studies in other organisms have shown that aminopropanol, derived from threonine, is the precursor of the chain linking dimethylbenzimidazole to the corrinoid ring of B12. Previously, a three-step pathway has been proposed for the synthesis of aminopropanol from threonine, including two enzymatic steps and a spontaneous nonenzymatic decarboxylation. We assayed the two enzymatic steps of the hypothetical pathway; cobD mutants are not defective in either. Furthermore, mutants blocked in one step of the proposed pathway continue to make B12. We conclude that the aminopropanol for B12 synthesis is not made by this pathway. Expression of a lac operon fused to the cobD promoter is unaffected by vitamin B12 or oxygen, both of which are known to repress the main cob operon, suggesting that the cobD gene is not regulated.     

A DFT study of tautomers of 3-amino-1-nitroso-4-nitrotriazol-5-one-2-oxide

We report herein the structure and explosive properties of the possible isomers of 3-amino-1-nitroso-4-nitrotriazol-5-one-2-oxide computed from the B3LYP/aug-cc-pVDZ level. The optimized structures, vibrational frequencies and thermodynamic values for triazol-5-one-N-oxides were obtained in the ground state. Several designed compounds have densities varying from 2.103 to 2.177 g/cm³. The detonation properties were evaluated by the Kamlet-Jacob equations based on the predicted density and the calculated heat of explosion. The detonation properties of triazol-5-one-N-oxides (D 9.87 to 10.11 km s^?1 and P 48.95 to 50.61 GPa) appear to be promising compared with those of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (D 9.20 km s^?1, P 42.0 Gpa) and octanitrocubane (D 9.90 km s^?1, P 48.45 GPa). The substitution of secondary amino hydrogen of the triazole ring by amino group shows better impact sensitivity/or stability however the model compounds seem to be highly sensitive.     

A concise synthesis of 5-amino-5-deoxyaldonic acids as monomers for the preparation of nylon 5

Saponification of 5-azido-5-deoxy-D-pentonolactones (ribo-, arabino-, xylo-) with NaOH gave the corresponding 5-azido-5-deoxyaldonic acids sodium salts which, after regeneration of the acid form followed by catalytic reduction, led to the target compounds in 98% overall yields.     

A facile synthesis of cis-4-amino-2-cyclopentene-1-methanol, a key intermediate for the synthesis of carbocyclic nucleosides

A number of carbocyclic nucleosides can be synthesized from (+/-)-cis-4-amino-2-cyclopentene-1-methanol (3). Carbocyclic amino alcohol 3 is a key intermediate that makes possible the efficient synthesis of the carbocyclic nucleosides. In this study we wish to report an efficient synthesis of carbocyclic amino alcohol 3 from inexpensive and readily available starting material. The synthetic route employed cyclopentadiene (4) as a starting material and proceeded in 38% overall yield through 6 steps involving a hetero Diels-Alder reaction and an aza-Claisen rearrangement.     

Isolation of 4-(1'-D-ribitylamino)-5-amino-2,6-dihydroxypyrimidine from a riboflavin-adenine-deficient mutant of Bacillus subtilis.

Studies were carried out to determine possible intermediates involved in the biosynthetic pathway of riboflavin, using resting cells of a riboflavin-adenine-deficient mutant, Bacillus subtilis AJ1988. The cells excreted 6,7-dimethyl-8-ribityllumazine, the end product in the biosynthetic pathway, into the incubation medium in large amounts. The addition of glyoxal caused a large accumulation of a green fluorescent compound; an inverse relation was observed between the formation of the lumazine and the concentration of glyoxal. Furthermore, added [2-14C]guanine effectively incorporated into the lumazine and the fluorescent compound in the same specific activity during incubation. The fluorescent compound was isolated, purified, and identified by paper chromatographic, fluorometric, and spectrophotometric analyses. It was proved to be 8-(1'-D-ribityl)lumazine, which appeared to have been formed by a reaction between glyoxal and a possible intermediate in the cells. Accordingly, 4-(1'-D-ribitylamino)-5-amino-2,6-dihydroxypyrimidine was concluded to be an immediate precursor of 6,7-dimethyl-8-ribityllumazine.