We have developed simple, aqueous strategies, that avoid the use of protecting groups and chromatography, for the preparation of a series of 5'-substituted guanosine derivatives.

The homoprotocatechuate 2,3-dioxygenase from Arthrobacter globiformis (MndD) catalyzes the oxidative ring cleavage reaction of its catechol substrate in an extradiol fashion. While this reactivity is more typically associated with nonheme iron enzymes, MndD exhibits an unusual specificity for manganese(II). MndD is structurally very similar to the iron(II)-dependent homoprotocatechuate 2,3-dioxygenase from Brevibacterium fuscum (HPCD), and we have previously shown that both MndD and HPCD are equally active towards substrate turnover with either Fe(II) or Mn(II) [J P Emerson, et al. (2008) Proc Natl Acad Sci USA, 105: 7347–7352]. However, expression of MndD in E. coli under aerobic conditions in the presence of excess iron results in the isolation of inactive blue-green Fe-substituted MndD (BG-FeMndD). Spectroscopic studies indicate that this form of Fe-substituted MndD contains an Fe(III) center with a bound catecholate, which is presumably generated by in vivo self-hydroxylation of a second-sphere tyrosine residue, as found for other self-hydroxylated nonheme iron oxygenases,. The absence of this modification in either the native Mn-containing MndD or Fe-containing HPCD suggests that the metal center of Fe-substituted MndD is able to bind and activate O2 in the absence of its substrate, employing a high-valent oxoiron oxidant to carry out the observed self-hydroxylation chemistry. These results demonstrate that the active site metal in MndD can support two dramatically different O2 activation pathways, further highlighting the catalytic flexibility of enzymes containing a 2-His-1-carboxylate facial triad metal binding motif.

Unsaturated oxyallyl cations with a suitably positioned alkene bond undergo 5-exo-cyclization with the formation of vinylcyclopentane derivatives. Alkyne analogues provide allenes. The reaction proceeds with a moderate to excellent level of stereoselectivity and allows for asymmetric induction in the reaction with chiral substrate.

The design, synthesis and biological evaluation of a novel C,D-spirolactone analogue of paclitaxel is described. This is the first paclitaxel analogue without an oxetane D-ring that shows a significant cytotoxic effect (activity one order of magnitude lower than paclitaxel). More importantly, its cytotoxicity is a result of a different mechanism of action, involving mTOR inhibition-dependent autophagy instead of G(2)/M cell cycle arrest-dependent apoptosis.

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details.

Domino reactions of ketones with molecular oxygen in the presence of potassium hydroxide and potassium t-butoxide afford cyclic hydroperoxy acetals (3,5-dihydroxy-1,2-dioxanes).

Summary Background: Heterobifunctional cross-linking agents are useful in both protein science and organic synthesis. Aminolysis of reactive esters in aqueous systems is often used in bioconjugation chemistry, but it must compete against hydrolysis processes. Here we study the kinetics of aminolysis and hydrolysis of 2-S-phosphorylacetate ester intermediates that result from displacement of bromide by a thiophosphate nucleophile from commonly used bromoacetate ester cross-linking agents. Results: We found cross-linking between uridine-5′-monophosphorothioate and D-glucosamine using N-hydroxybenzotriazole and N-hydroxysuccinimde bromoacetates to be ineffective. In order to gain insight into these shortfalls, 2-S-(5′-thiophosphoryluridine)acetic acid esters were prepared using p-nitrophenyl bromoacetate or m-nitrophenyl bromoacetate in combination with uridine-5′-monophosphorothioate. Kinetics of hydrolysis and aminolysis of the resulting p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates were determined by monitoring the formation of phenolate ions spectrophotometrically as a function of pH. The p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates showed similar reactivity profiles despite the significant difference in the pK aH values of their nitrophenolate leaving groups. Both were more reactive with respect to hydrolysis and aminolysis in comparison to their simple acetate progenitors, but their calculated selectivity towards aminolysis vs hydrolysis, while reasonable, would not lead to clean reactions that do not require purification. Extrapolations of the kinetic data were used to predict leaving group pK a values that could lead to improved selectivity towards aminolysis while retaining reasonable reaction times. Conclusions: Both p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates show some selectivity towards aminolysis over hydrolysis, with the m-nitrophenolate system displaying slightly better selectivity. Extrapolation of the data for hydrolysis and aminolysis of these esters suggests that the use of readily accessible trifluoroethyl 2-S-(5′-thiophosphoryluridine)acetate with a leaving group pK aH of 12.4 should afford better selectivity while maintaining reasonable reaction times. Kinetically, p- and m-nitrophenyl 2-S-(5′-thiophosphoryluridine)acetates show similar properties to o-nitrophenyl 2-S-ethylacetate, and show no evidence for intramolecular catalysis of hydrolysis or aminolysis by the phosphoryl groups.

(2013) 'Aqueous synthesis of N,S,-dialkylthiophosphoramidates : design, optimisation and application to library construction and antileishmanial testing. ', Organic and biomolecular chemistry., 11 (16). pp. 2660-2675. Further information on publisher's website:Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We recently reported the use of PSCl 3 for the thiophosphorylation of alkylamines where the resulting Nthiophosphoramidate ions could be readily S-alkylated (Chem. Commun., 2011, 47, 6156-6158.). Herein 10 we report the development of this methodology using amino acid, amino sugar, aminonucleoside and aniline substrates. The hydrolysis properties of N-thiophosphoramidate ions and their reactivities towards alkylating agents are also explored. In addition, we demonstrate the application of our approach to the preparation of a small library of compounds, including quinoline-based N,S-dialkylthiophosphoramidates which were tested for antileishmanial activity.15