The novel synthesis of a [6:5:6] linear isoguanosine type tricyclic nucleoside using carbonyl sulfide

The novel one-step synthesis of a fused pyrimidin-2-one-4-thione derivative from an $\text{o}$-aminonitrile using carbonyl sulfide is described.     

A computer simulation of elastic effects in the two-roll mill problem

In a previous paper consideration was given to the flow of a generalised Newtonian liquid between contra-rotating cylinders — the so-called two-roll mill problem. We present here an extension to that work in which we consider the effect of elasticity on the flow. An Oldroyd three-constant model is used to characterize the fluid properties and a finite-element method used to solve the relevant equations. Results are presented for different speeds of rotation of the cylinders and for various values of the fluid parameters. A comparison is made between the effects of elasticity and of shear-thinning on the flow patterns around the cylinders.     

Predicting charmonium and bottomonium spectra with a quark harmonic oscillator

We present a simple application of the three-dimensional harmonic oscillator which should provide a very nice particle physics example to be presented in introductory undergraduate quantum mechanics course. The idea is to use the nonrelativistic quark model to calculate the spin-averaged mass levels of the charmonium and bottomonium spectra.     

A basic strategy for the thermal stability assessment of pharmaceutical synthetic intermediates and products

A relatively simple strategy is described for the thermal hazard screening of isolated synthetic intermediates and products, as employed within the Research Division of a major pharmaceutical company.Differential scanning calorimetry under carefully controlled conditions is used as a screening technique to reveal any propensity a material may have towards significant exothermic decomposition. Suspect samples are further investigated via combustion tests, such as train firing studies or flash point determinations, and via accelerating rate calorimetry; data obtained facilitate characterisation with regard to ignition/flammability properties and bulk stability. A real-life case study is presented to illustrate the application of this methodology to an unstable synthetic intermediate for which safe conditions for processing and bulk storage are derived.

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Zusammenfassung Es wird eine relativ einfache Methode zur Ermittlung der WÄrmeempfindlichkeit isolierter synthetischer Zwischenprodukte und Endprodukte beschrieben, wie sie innerhalb eines gro\en Arzneimittelunternehmens vorkommen. Als Screening-Verfahren wurde DSC unter sorgfÄltig kontrollierten Bedingungen angewendet, um jegliche Neigungen festzustellen, die eine Substanz bezüglich einer signifikanten exothermen Zersetzung haben kann. VerdÄchtige Proben wurden weiterhin mittels Verbrennungstests und ARC untersucht; die ermittelten Angaben erleichtern die Charakterisierung im Hinblick auf Entzündungs- und Entflammbarkeitseigenschaften sowie MassebestÄndigkeit. Es wird weiterhin eine in der Praxis durchgeführte Studie beschrieben, um die Anwendung dieses Verfahrens bei einem unbestÄndigen synthetischen Zwischenprodukt zu illustrieren, für welches sichere Verfahrens- und Lagerungsbedingungen ermittelt wurden.

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Grateful thanks are due to the following for helpful discussions during the preparation of this paper; Mr. C. E. Valder, Dr. M. E. Morris, Mr. A. J. Baxter, Mr. D. J. O'Rouke (SmithKline Beecham Pharmaceuticals) and Mr. P. G. Lambert (Sterling Organics Ltd). The experimental assistance of the following is also gratefully acknowledged; Mr. L. R. Brockhurst and Miss S. A. Smith (SmithKline Beecham Pharmaceuticals).     

Structural and Biochemical Analysis of Protein–Protein Interactions Between the Acyl‐Carrier Protein and Product Template Domain

In fungal non‐reducing polyketide synthases (NR‐PKS) the acyl‐carrier protein (ACP) carries the growing polyketide intermediate through iterative rounds of elongation, cyclization and product release. This process occurs through a controlled, yet enigmatic coordination of the ACP with its partner enzymes. The transient nature of ACP interactions with these catalytic domains imposes a major obstacle for investigation of the influence of protein–protein interactions on polyketide product outcome. To further our understanding about how the ACP interacts with the product template (PT) domain that catalyzes polyketide cyclization, we developed the first mechanism‐based crosslinkers for NR‐PKSs. Through in vitro assays, in silico docking and bioinformatics, ACP residues involved in ACP–PT recognition were identified. We used this information to improve ACP compatibility with non‐cognate PT domains, which resulted in the first gain‐of‐function ACP with improved interactions with its partner enzymes. This advance will aid in future combinatorial biosynthesis of new polyketides.     

Synthesis and fate of o-carboxybenzophenones in the biosynthesis of aflatoxin

o-Carboxybenzophenones have long been postulated to be intermediates in the oxidative rearrangement of anthraquinone natural products to xanthones in vivo. Many of these Baeyer-Villiger-like cleavages are believed to be carried out by cytochrome P450 enzymes. In the biosynthesis of the fungal carcinogen, aflatoxin, six cytochromes P450 are encoded by the biosynthetic gene cluster. One of these, AflN, is known to be involved in the conversion of the anthraquinone versicolorin A (3) to the xanthone demethylsterigmatocystin (5) en route to the mycotoxin. An aryl deoxygenation, however, also takes place in this overall transformation and is proposed to be due to the requirement that an NADPH-dependent oxidoreductase, AflM, be active for this process to take place. What is known about other fungal anthraquinone --> xanthone conversions is reviewed, notably, the role of the o-carboxybenzophenone sulochrin (25) in geodin (26) biosynthesis. On the basis of mutagenesis experiments in the aflatoxin pathway and these biochemical precedents, total syntheses of a tetrahydroxy-o-carboxybenzophenone bearing a fused tetrahydrobisfuran and its 15-deoxy homologue are described. The key steps of the syntheses entail rearrangement of a 1,2-disubstituted alkene bearing an electron-rich benzene ring under Kikuchi conditions to give the 2-aryl aldehyde 43 followed by silyltriflate closure to a differentially protected dihydrobenzofuran 44. Regiospecific bromination, conversion to the substituted benzoic acid, and condensation with an o-bromobenzyl alcohol gave esters 47 and 50. The latter could be rearranged with strong base, oxidized, and deprotected to the desired o-carboxybenzophenones. These potential biosynthetic intermediates were examined in whole-cell and ground-cell experiments for their ability to support aflatoxin formation in the blocked mutant DIS-1, defective in its ability to synthesize the first intermediate in the pathway, norsolorinic acid. Against expectation, neither of these compounds was converted into aflatoxin under conditions where the anthraquinones versicolorin A and B readily afforded aflatoxins B1 and B2. This outcome is evaluated further in a companion paper appearing later in this journal.     

The synthesis of 2-azainosine and related derivatives by ring annulation of imidazole nucleosides

The synthesis of 7-(β-D-ribofuranosyl)imidazo[4,5-d]-v-triazin-4-one ( 6b , 2-azainosine) and 5-(β-D-ribofuranosyl)imidazo[4,5-d]-v-triazin-4-one ( 4b ) have been achieved for the first time by direct diazotization of AICA riboside ( 5b ) and iso-AICA riboside ( 3b ), respectively. The conditions required for cyclization of the model methyl bases, 3a and 5a , as well as the nucleosides 3b , 5b , and 7 are described.     

Facile synthesis of 1-substituted 2-amino-3-cyanopyrroles: new synthetic precursors for 5,6-unsubstituted pyrrolo[2,3-d]pyrimidines

1-Benzyl-3-cyanopyrrole-2-carbonyl azide (5) underwent a Curtius rearrangement followed by quenching with alcohols to form the corresponding carbamates (6a-c). The carbamates 6a,b were unblocked to give the desired 2-amino-1-benzyl-3-cyanopyrrole (1a). A more facile procedure was subsequently developed for the synthesis of 1-substituted 2-amino-3-cyanopyrroles. N-Substituted aminoacetaldehyde dimethyl acetals (7a-c) were condensed with malononitrile in the presence of p-toluenesulfonic acid monohydrate to afford the corresponding 1-substituted 2-amino-3-cyanopyrroles (1a-c).     

Synthesis of 8-amino-4-methylthio-6-methyl-2-(β-D-ribofuranosyl)-2,6-dihydro-1,2,3,5,6,7-hexaazaacenaphthylene and an unusual reductive ring-opening of the 1,2,3,5,6,7-hexaazaacenaphthylene ring system

The tricyclic nucleoside 8-amino-4-methylthio-6-methyl-2-(β-D-ribofuranosyl)-1,2,3,5,6,7-hexaazaacenaphthylene ( 3 ) was synthesized from 3-cyano-4,6-bis(methylthio)-1-(β-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidine ( 1 ). Attempts to synthesize 8-amino-6-methyl-2-(β-D-ribofuranosyl)-1H-2,6-dihydro-1,2,3,5,6,7-hexaazaacenaphthylene ( 5 ) ([an aza analog of 6-amino-4-methyl-8-(β-D-ribofuranosyl)-1,3,4,5,8-pentaazaacenaphthylene (TCN)], which is a potent antitumor agent), by the treatment of 3 with Raney nickel did not afford the desired aza analog of TCN. Instead, it was established that a reductive cleavage of the pyridazine moiety of 3 had occurred to give 4-methylamino-6-methylthio-1-(β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidine-3-carboxamidine ( 6 ). Assuming that solubility was a problem in the reductive step, the isopropylidene derivative of 3 , 8-amino-6-methyl-4-methylthio-2-(2,3-O-isopropylidene-β-D-ribofuranosyl)-2,6-dihydro-1,2,3,5,6,7-hexaazaacenaphthylene ( 8 ), was treated with Raney nickel, only to observe that a similar reductive ring cleavage of 8 had occurred to afford 4-methylamino-6-methylthio-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidine-3-carboxamidine ( 10 ) and 4-methylamino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidine-3-carboxamidine ( 11 ). Structural assignments for all products were established by physico-chemical procedures.     

An Investigation on the thermolytic conversions of 5-Diazouracils into 1,2,3-Triazoles

The thermolysis of 5-diazo-6-methoxy-1-methyl-1,6-dihydrouracil ( 1 ) has afforded methyl N-(1-methyl-1,2,3-triazol-4-oyl)carbamate ( 2 ), bis-(1-methyl-1,2,3-triazol-4-oyl)amine ( 3 ) and di-methylcarbimate ( 4 ). The reaction was shown to proceed with the initial formation of 2 followed by a subsequent disproportionation of 2 to give 3 and 4 . A similar thermolysis of 5-diazo-6-ethoxy-1-methyl-1,6-dihydrouracil ( 9 ) gave ethyl N-(1-methyl-1,2,3-triazol-4-oyl)car-bamate ( 10 ) as the sole product. Double labeling experiments have indicated that a major pathway for these reactions involves an intermolecular transfer of the C-6 substituent to the C-2 position.