Single-step conversion of N-benzyl, N-trityl and N-diphenylmethyl amines to t-butyl carbamates using polymethylhydrosiloxane

t-Butyl carbamates were obtained efficiently in high yields from the corresponding N-benzyl, N-trityl and N-diphenylmethyl precursors in a single-step reductive transformation employing polymethylhydrosiloxane and di-t-butyl dicarbonate under Pd(OH)₂/C catalysis.     

Synthesis of 4,6-disubstituted-7-β-D-ribofuranosyl- and arabinofuranosylpyrazolo[3,4-d]pyrimidines and certain related ribonucleosides

Several disubstituted pyrazolo[3,4-d]pyrimidine, pyrazolo[1,5-a]pyrimidine and thiazolo[4,5-d]pyrimidine ribonucleosides have been prepared as congeners of uridine and cytidine. Glycosylation of the trimethylsilyl (TMS) derivative of pyrazolo[3,4-d]pyrimidine-4,6(1H,5H,7H)-dione ( 4 ) with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose ( 5 ) in the presence of TMS triflate afforded 7-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)pyrazolo-[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 6 ). Debenzoylation of 6 gave the uridine analog 7-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 3 ), identical with 7-ribofuranosyloxoallopurinol reported earlier. Thiation of 6 gave 7 , which on debenzoylation afforded 7-β-D-ribofuranosyl-6-oxopyrazolo[3,4-d]pyrimidine-4(1H,5H)-thione ( 8 ). Ammonolysis of 7 at elevated temperature gave a low yield of the cytidine analog 4-amino-7-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidin-6(1H)-one ( 11 ). Chlorination of 6 , followed by ammonolysis, furnished an alternate route to 11 . A similar glycosylation of TMS-4 with 2,3,5-tri-O-benzyl-α-D-arabinofuranosyl chloride ( 12 ) gave mainly the N7-glycosylated product 13 , which on debenzylation provided 7-β-D-arabinofuranosylpyrazolo[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 14 ). 4-Amino-7-β-D-arabinofuranosyl-pyrazolo[3,4-d]pyrimidin-6(1H)-one ( 19 ) was prepared from 13 via the C4-pyridinium chloride intermediate 17 . Condensation of the TMS derivatives of 7-hydroxy- ( 20 ) or 7-aminopyrazolo[1,5-a]pyrimidin-5(4H)-one ( 23 ) with 5 in the presence of TMS triflate gave the corresponding blocked nucleosides 21 and 24 , respectively, which on deprotection afforded 7-hydroxy- 22 and 7-amino-4-β-D-ribofuranosylpyrazolo[1,5-a]pyrimidin-5-one ( 25 ), respectively. Similarly, starting either from 2-chloro ( 26 ) or 2-aminothiazolo[4,5-d]pyrimidine-5,7-(4H,6H)-dione ( 29 ), 2-amino-4-β-D-ribofuranosylthiazolo[4,5-d]pyrimidine-5,7(6H)-dione ( 28 ) has been prepared. The structure of 25 was confirmed by single crystal X-ray diffraction studies.     

Block copolymerization initiated by Mn(III)-poly(ethylene glycol) redox system — general features and kinetics

The kinetics and mechanism of thermal polymerization of acrylonitrile initiated by Mn(III) pyrophosphate — poly(ethylene glycol) (PEG, molecular weight 6000) redox system in aqueous sulfuric acid medium was studied in the temperature range 30–60°C. The overall rates of polymerization and the disappearance of Mn³⁺ were determined. The polymerization was initiated by the organic free radical produced from the Mn³⁺-PEG reaction and the termination was by the metal ions. The rate of polymerization of acrylonitrile was found to be directly proportional to the square of the monomer concentration and first power of PEG concentration, and inversely proportional to the concentration of Mn³⁺. The rate of manganic ion disappearance was found to be directly proportional to manganic ion concentration and PEG concentration, and independent of the monomer concentration. Based on these observations, a plausible reaction scheme was suggested and suitable kinetic expressions were evaluated.     

Synthesis of hapten-phosphoramidites from 2′-deoxyuridine

A total of 11 novel phosphoramidites, 3a-d, 4a-d and 14a-c were prepared from 2′-deoxyuridine functionalized at 5 and 6-position of the pyrimidine ring with hapten reporter groups, e.g. adamantane, carbazole, dansyl and dabsyl, suitable for use in immunodetection nucleic acid testing assays.     

Syntheses and characterization of poly(benzimidazolyl) thiaxanthones

Novel polybenzimidazoles containing thiaxanthone heterocyclic units were synthesised from 2,7-thiaxanthonedicarboxylic acid-5,5′-dioxide and 2,8-thiaxanthonedicarboxylic acid-5,5′-dioxide and two aromatic tetramine hydrochlorides by PPA solution polycondensation in 60–70% yield. Two model compounds, 2,7-bis(2-benzimidazolyl)thiaxanthone-5,5′-dioxide and 2,8-bis(2-benzimidazolyl)thiaxanthone-5,5′-dioxide, were prepared and characterized by spectral methods. The polybenzimidazoles have inherent viscosities in the range 1.13–1.50 dL/g and decomposition temperatures of 495–560°C. The effect of thiaxanthone units on polymer properties are discussed.     

(Vapor + liquid) equilibria of the binary mixtures of m-cresol with C1-C4 aliphatic alcohols at 95.5 kPa

Bubble point temperatures at 95.5 kPa, over the entire composition range, are measured for the binary mixtures formed by m-cresol with: methanol, ethanol, 1-propanol, 2-propanol, and n-, iso-, sec-, and tert-butanols - using a Swietoslawski-type ebulliometer. The liquid phase composition - bubble point temperature measurements are well represented by the Wilson model. (Vapor + liquid) equilibria predicted from the model are presented.     

A note on a result of Zolotarev and Bernstein

In this note we obtain error bounds to x²ⁿ⁺¹–x²ⁿ on [–1, 1] by polynomials of degree at most (2n–1). The result proved here improves and extends some of the known results of Zolotarev and Bernstein. The proof presented here is different (and simple) from the one adopted by Zolotarev and Bernstein.     

A simple stereocontrolled synthesis of salinosporamide A

A simple and effective stereocontrolled synthesis of salinosporamide A has been developed. This process, the first synthesis of salinosporamide A, is capable of providing the compound in substantial quantities for further biological studies. Salinosporamide A was of special interest as a synthetic target because of its potent in vitro cytotoxic activity against many tumor cell lines (IC(50) values of 10 nM or less).     

Ciprofloxacin-protected gold nanoparticles

The antibacterial drug ciprofloxacin (cfH) has been used to protect gold nanoparticles of two different mean diameters, 4 and 20 nm. The protection is complete with about 65 and 585 cfH molecules covering 4 and 15 nm particles, respectively. The nature of binding has been investigated by several analytical techniques. The nitrogen atom of the NH moiety of piperazine group binds on the gold surface, as revealed by voltammetric and spectroscopic studies. The cfH-adsorbed particles are stable in the dry state as well as at room temperature, and as a result, redispersion is possible. The rate of release of the drug molecule from the nanoparticles is more in the basic medium than in pure water, and the kinetics depend on the size of the particle; faster desorption is seen in smaller particles. The bound cfH is fluorescent, and this property could be used in biological investigations. This study shows that metal nanoparticles could be useful carriers for cfH and fluoroquinolone molecules. Most of the bound molecules could be released over an extended period of time.