Dinesh K. Dikshit

Titanium enolates from pyroglutamates: Exclusive formation of 4-α aldol adducts

Abstract Aldol reactions of pyroglutamate derived titanium enolate give exclusively 4-α adducts.

Self reproduction of chirality in pyroglutamates: Reactions at α- position with electrophiles☆

Abstract Condensation of pyroglutamic acid with trimethylacetaldehyde gave a bicyclic derivative which on deprotonation with LiHMDS and reaction with electrophiles gives chiral α-substituted pyroglutamate derivatives.

Cycloaddition–hydrogenolysis strategy for the synthesis of 2,4-disubstituted pyroglutamates ☆

Abstract 1,3-Dipolar addition of amino acid derived dipoles with menthyl acrylate followed by hydrogenolysis of the adduct gives chiral 2-α-substituted-4-α-arylmethyl-pyroglutamates.

1,2-addition of ∝-amino acid derivatives to conjugated aldehydes: synthesis of β -substituted serines

Abstract Reaction of C,N-dianions of N-acyl ∝ -amino acid esters with conjugated aldehydes at -78°C give threo - and erythro -β-substituted serine derivatives in excellent yields.

Quantification of Cells with Specific Phenotypes I: Determination of CD4+ Cell Count Per Microliter in Reconstituted Lyophilized Human PBMC Prelabeled with Anti-CD4 FITC Antibody

A surface‐labeled lyophilized lymphocyte (sLL) preparation has been developed using human peripheral blood mononuclear cells prelabeled with a fluorescein isothiocyanate conjugated anti‐CD4 monoclonal antibody. The sLL preparation is intended to be used as a reference material for CD4+ cell counting including the development of higher order reference measurement procedures and has been evaluated in the pilot study CCQM‐P102. This study was conducted across 16 laboratories from eight countries to assess the ability of participants to quantify the CD4+ cell count of this reference material and to document cross‐laboratory variability plus associated measurement uncertainties. Twelve different flow cytometer platforms were evaluated using a standard protocol that included calibration beads used to obtain quantitative measurements of CD4+ T cell counts. There was good overall cross‐platform and counting method agreement with a grand mean of the laboratory calculated means of (301.7 ± 4.9) μL−1 CD4+ cells. Excluding outliers, greater than 90% of participant data agreed within ±15%. A major contribution to variation of sLL CD4+ cell counts was tube to tube variation of the calibration beads, amounting to an uncertainty of 3.6%. Variation due to preparative steps equated to an uncertainty of 2.6%. There was no reduction in variability when data files were centrally reanalyzed. Remaining variation was attributed to instrument specific differences. CD4+ cell counts obtained in CCQM‐P102 are in excellent agreement and show the robustness of both the measurements and the data analysis and hence the suitability of sLL as a reference material for interlaboratory comparisons and external quality assessment.

Assessement of the pharmacokinetics, tissue distribution and excretion studies of a novel antiplatelet agent S007-867, following administration to rats

S007-867 is a promising novel antiplatelet agent with better efficacy and lesser bleeding risk than existing agents. The present study investigated the absorption, tissue distribution, and excretion of S007-867 in rat model for further advancement of the molecule. A simple and robust ultra fast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS) bioanalytical method was used to determine S007-867 in various matrices. Following oral administration, the compound was quickly dispersed in the various tissues and peak concentration levels were achieved within 0.5-1 h. Overall, exposure of drug, i.e., AUC in different tissues was found in the order of small intestine > liver > heart > spleen > lungs > kidney > brain. The total recoveries of the S007-867 within 96 h were 3.36% in urine and faeces. This might be due to a first-pass effect by the liver and intestine as most of the drug was eliminated in metabolite form. These findings provide a crucial information about further development of S007-867 as antithrombotic agent. Copyright

Pharmacokinetics and tissue distribution study of novel potent antiplatelet agent S007-867 in mice using HPLC-MS/MS

Abstract 1. S007-867 is a novel antiplatelet agent that shows promising in vitro and in vivo efficacy. For further development and better pharmacological elucidation, we characterized pharmacokinetics and tissue distribution of S007-867 in a mouse model. 2. A sensitive, selective and robust LC-MS/MS method was developed and validated in the mouse plasma and tissue for quantification of S007-867. The chromatographic separation was performed on Waters Symmetry Shield C18 column (150 × 4.6 mm, 5 µm) using methanol and ammonium acetate buffer. 3. S007-867 was rapidly absorbed and distributed to various tissues. Following single oral administration of S007-867 in the mouse, the concentration was in the order of C intestine > C liver > C kidney > C heart > C spleen > C lungs > C brain. Tissue to plasma area under the plasma curve ratio suggested that the maximum amount of drug was found in the intestine and liver. Half life of S007-867 was found longer in the heart (8.08 h), spleen (∼ 7.94 h) and kidney (∼ 15.41 h) as compared with other tissues. 4. The preclinical pharmacokinetics and tissue distribution data obtained using this LC-MS/MS method are expected to assist the future clinical investigations of S007-867 as a promising antiplatelet agent.

Synthesis of N -[3′-(acetylthio)alkanoyl] and N -[3′-mercaptoalkanoyl]-4-α(s)-(phenylmethyl) pyroglutamic acids and prolines as potent ACE inhibitors

Angiotensin converting enzyme (ACE) inhibitors have emerged as a revolution in antihypertensive therapy. Introduction of captopril, the first rationally designed ACE inhibitor, has encouraged researchers all over the world to design and synthesize target molecules controlling hypertension based on these lines. It has been observed that replacing proline part of captopril with 4-substituted prolines or 5-oxo-prolines led to significant enhancement in ACE inhibitory activity, and this observation prompted us to design and synthesize N-acyl 4-substituted pyroglutamates and prolinates with the objective of developing therapeutically better ACE inhibitors. Herein we describe an easy approach for N-acylation of 4-α(S)-(phenylmethyl) pyroglutamates with the aim of synthesizing N-[3′-(acetylthio)alkanoyl] and N-[3′-mercaptoalkanoyl]-4-α-(s)-(phenylmethyl) pyroglutamic acids and prolines as ACE inhibitors.Graphical Abstract

Metabolism of CDRI-85/92, a new potent anti-ulcer agent, involving cis-trans conversion.

CDRI 85/92, an anti-ulcer drug, is a new proton pump inhibitor, currently in an advanced stage of drug development. To know more about the drug it was our objective to delineate/identify the metabolic pathway as well as the enzymes responsible for the formation of metabolites. Metabolism of CDRI-85/92 (cis-5-styryl-2-oxazolidinone-4-carboxylic acid) was investigated in rat liver cellular fractions (S9, microsomes and cytosol) using reverse-phase HPLC and mass spectrometry techniques. Two major metabolites were produced by rat liver S9 fractions and reducing factor generating system from either untreated rats or phenobarbitone (PB)-pretreated rats. Incubation of CDRI-85/92 with postmitochondrial fraction (S9) for 24 h resulted in a cis to trans conversion (metabolite M2). Further cis-trans metabolizing capacity was measured separately in the cytosolic and microsomal fractions. Incubation with the cytosolic fraction resulted in an increased rate of cis-trans conversion, while the microsomal fraction showed no cis to trans conversion, thereby restricting the cis to trans conversion to Phase II enzymes, which are mainly located in the cytosol. Studies with PB-pretreated rat liver S9 fractions resulted in an increased rate of cis to trans conversion. Another metabolite was also present (M1) which was identified as an oxygenated metabolite by mass spectrometry. The major urinary metabolite from CDRI-85/92-treated Sprague-Dawley rats (20 mg/kg p.o.) was identified as M2. Studies using sulfobromophthalein and N-ethylmaleimide, as specific inhibitors of GST, showed a complete absence of metabolism, thus indicating the involvement of GST in the metabolism of CDRI-85/92. This study will be helpful in providing clues about factors influencing the bioavailability of CDRI-85/92 as well as drug-drug interactions.

Remote O, C-dianion chemistry of pyroglutamates: Reaction at C-4 with electrophiles☆

Abstract O, C-Di-lithio di-anions derived from N-substituted pyroglutamic acids react with electrophiles to give C-4 α- substituted products.