Rapid quantification of total genomic DNA methylation degree by short-end injection capillary zone electrophoresis

We propose a new capillary zone electrophoresis method applying short-end injection technique for the fast evaluation of methylcystosine/total cytosine ratio after acidic DNA hydrolysis. By short-end injection and by using a 100 mmol/l Tris solution titrated with 1 mol/l phosphoric acid to pH 3.75 as background electrolyte, cytosine and methylcytosine were separated with a good resolution in less than 1.5 min. Stepwise multiple linear regression with DNA methylation degree as the dependent variable and age, cysteine, homocysteine and methionine as independent variables, showed a negative association with age and that total cysteine is the most important determinant of DNA methylation.     

Multistep Continuous Flow Synthesis of Isolable NH2-Sulfinamidines via Nucleophilic Addition to Transient Sulfurdiimide

The growing interest in novel sulfur pharmacophores led to recent advances in the synthesis of some S(IV) and S(VI) motifs. However, preparation and isolation of uncommon primary sulfinamidines, the aza-analogues of sulfinamides, is highly desirable. Here we report a multistep continuous flow synthesis of poorly explored NH₂-sulfinamidines by nucleophilic attack of organometallic reagents to in situ prepared N-(trimethylsilyl)-N-trityl-λ⁴-sulfanediimine (Tr−N=S=N−TMS). The transformation can additionally be realized under mild conditions, at room temperature, via a highly chemoselective halogen-lithium exchange of aryl bromides and iodides with n-butyllithium. Moreover, the synthetic potential of the methodology was assessed by exploring further manipulations of the products and accessing novel S(IV) analogues of celecoxib, tasisulam, and relevant sulfinimidoylureas.     

Tropical Hurwitz numbers

Hurwitz numbers count genus g, degree d covers of ℙ¹ with fixed branch locus. This equals the degree of a natural branch map defined on the Hurwitz space. In tropical geometry, algebraic curves are replaced by certain piece-wise linear objects called tropical curves. This paper develops a tropical counterpart of the branch map and shows that its degree recovers classical Hurwitz numbers. Further, the combinatorial techniques developed are applied to recover results of Goulden et al. (in Adv. Math. 198:43–92, 2005) and Shadrin et al. (in Adv. Math. 217(1):79–96, 2008) on the piecewise polynomial structure of double Hurwitz numbers in genus 0.     

Combinatorial sums and implicit Riordan arrays

In this paper we present the theory of implicit Riordan arrays, that is, Riordan arrays which require the application of the Lagrange Inversion Formula to be dealt with. We show several examples in which our approach gives explicit results, both in finding closed expressions for sums and, especially, in solving classes of combinatorial sum inversions.     

Rotational barriers of biphenyls having heavy heteroatoms as ortho-substituents: experimental and theoretical determination of steric effects

The free energies of activation for the aryl-aryl rotation of 17 biphenyl derivatives, bearing a heavy heteroatom (S, Se, Te, P, Si, Sn) as ortho substituent, have been measured by variable temperature NMR. These numbers, so called B values, represent a meaningful measure of the steric hindrance exerted by the selected substituents. DFT computations match quite satisfactorily the experimental barriers and the ground state geometries as well (determined, in two cases, by X-ray diffraction). The present values extend the available list of B values and thus provide an enlarged basis for the compilation of the space requirements of standard substituents, based solely on experimental determinations.     

Development and validation of a high‐performance liquid chromatography–tandem mass spectrometry method for the determination of the novel proteasome inhibitor CEP‐18770 in human plasma and its application in a clinical pharmacokinetic study

CEP‐18770, [(1R)‐1‐{[(2S,3R)‐3‐hydroxy‐2‐{[(6‐phenyl‐2‐pyridinyl)carbonyl]amino}butanoyl]amino}‐3‐methylbutyl]boronic acid, is a novel proteasome inhibitor, now under early clinical evaluation as an anticancer agent. To investigate its clinical pharmacokinetics, a high‐performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) method was developed and validated to measure the drug in human plasma, based on simple protein precipitation with acetonitrile after the addition of irbesartan as internal standard. The method requires a small volume of sample (100 µl) and is rapid and selective, allowing good resolution of peaks in 5 min. It is sensitive, precise and accurate, with overall precision, expressed as coefficient of variation (CV%), always < 10.0%, accuracy in the range 93.8–107.7% and high recovery, close to 100%. The limit of detection is 0.01 ng/ml and the lower limit of quantitation (LLOQ) is 0.20 ng/ml. The assay was validated in the range from the LLOQ up to 50.00 ng/ml. This is the first method developed and validated for analyzing a proteasome inhibitor with a boronic‐acid‐based structure in human plasma. The method was successfully applied to study the pharmacokinetics of CEP‐18770 in cancer patients with solid tumors or multiple myeloma who had received the drug as a short intravenous bolus during the initial Phase I trial. Copyright © 2010 John Wiley & Sons, Ltd.