Investigation of thermochemical Features of Gamma Irradiated Tryptophan Stereoisomers

In this work, the use of differential scanning calorimetry (DSC) is demonstrated as a powerful technique that can provide accurate thermodynamic property values of nutritional supplements such as tryptophan. Nutritional supplements require a decontamination procedure and irradiation appears as a promising technique for this purpose. The valuable properties of tryptophan for food and pharmaceutical industry as dietary supplement have led to increasing interest in its technological behaviour. L-, D- isomers and DL-racemic mixture of tryptophan irradiated and non-irradiated were studied by DSC. Irradiation was performed at room temperature with gamma radiations using a 137Cs source, the irradiation dose range was between 0.6- 10 kGy. Two steps decomposition pattern for both irradiated and non-irradiated samples up to 350 oC was found. Fourier transform infrared spectroscopic studies were performed. The obtained results indicate that the irradiation process does not inhibit the thermal properties of tryptophan when irradiated up to 10 kGy. The HPLC method was employed to evidence the degradation of the irradiated material. Resumen. En este trabajo, se demuestra el uso de calorimetría diferencial de barrido (DSC) como una técnica poderosa que puede proporcionar valores precisos de propiedades termodinámicas de suplementos nutricionales como el triptófano. Los suplementos nutricionales requieren un procedimiento de descontaminación y la irradiación aparece como una técnica prometedora para este propósito. Las valiosas propiedades del triptófano para la industria alimentaria y farmacéutica como suplemento dietético han provocado un creciente interés por su comportamiento tecnológico. Los isómeros L-, D- y la mezcla racémica DL- de triptófano irradiado y no irradiado fueron estudiados por DSC. La irradiación se realizó a temperatura ambiente con radiaciones gamma utilizando una fuente de 137Cs, el rango de dosis de irradiación estuvo entre 0.6 - 10 kGy. Se encontró un patrón de descomposición de dos pasos para muestras irradiadas y no irradiadas hasta 350 ºC. Se realizaron estudios espectroscópicos de infrarrojos por la transformada de Fourier. Los resultados obtenidos indican que el proceso de irradiación no inhibe las propiedades térmicas del triptófano cuando se irradia hasta 10 kGy. Se empleó el método HPLC para evidenciar la degradación del material irradiado.

Cryoprotective activities of FK20, a human genome-derived intrinsically disordered peptide against cryosensitive enzymes without a stereospecific molecular interaction

Background Intrinsically disordered proteins (IDPs) have been shown to exhibit cryoprotective activity toward other cellular enzymes without any obvious conserved sequence motifs. This study investigated relationships between the physical properties of several human genome-derived IDPs and their cryoprotective activities. Methods Cryoprotective activity of three human-genome derived IDPs and their truncated peptides toward lactate dehydrogenase (LDH) and glutathione S-transferase (GST) was examined. After the shortest cryoprotective peptide was defined (named FK20), cryoprotective activity of all-D-enantiomeric isoform of FK20 (FK20-D) as well as a racemic mixture of FK20 and FK20-D was examined. In order to examine the lack of increase of thermal stability of the target enzyme, the CD spectra of GST and LDH in the presence of a racemic mixture of FK20 and FK20-D at varying temperatures were measured and used to estimate Tm. Results Cryoprotective activity of IDPs longer than 20 amino acids was nearly independent of the amino acid length. The shortest IDP-derived 20 amino acid length peptide with sufficient cryoprotective activity was developed from a series of TNFRSF11B fragments (named FK20). FK20, FK20-D, and an equimolar mixture of FK20 and FK20-D also showed similar cryoprotective activity toward LDH and GST. Tm of GST in the presence and absence of an equimolar mixture of FK20 and FK20-D are similar, suggesting that IDPs’ cryoprotection mechanism seems partly from a molecular shielding effect rather than a direct interaction with the target enzymes.

Distribution and Quantification of 1,2-Propylene Glycol Enantiomers in Baijiu

Enantiomers of 1,2-Propylene glycol (1,2-PG) were investigated in 64 commercial Chinese Baijiu including soy sauce aroma-type Baijiu (SSB), strong aroma-type Baijiu (STB), and light aroma-type Baijiu (LTB), via chiral gas chromatography (β-cyclodextrin). The natural enantiomeric distribution and concentration of 1,2-PG in various baijiu were studied to evaluate whether the distribution and content of the two isomers of 1,2-PG were correlated with the aroma type and storage year. The results showed that 1,2-PG has a high enantiomeric ratio and the (S)-configuration predominated in SSB. The average S/R enantiomeric ratio of this compound in SSB was approximately 87:13 (±3.17), with an average concentration of 52.77 (±23.70) mg/L for the (S)-configuration and 8.72 (±3.63) mg/L for the (R)-enantiomer. The (R)-configuration was predominant in the STB, whereas neither (S) nor (R)-form of 1,2-PG were detected in LTB. The content of the two configurations of 1,2-PG in the JSHSJ vintage of SSB showed a wave variation, with an average S/R enantiomeric ratio of 89:11 (±1.15). The concentration of (R)-1,2-PG in XJCTJ vintage liquors showed an upward and then downward trend with aging time, with an overall downward trend, and the concentration of (S)-form showed a wavy change with an overall upward trend. Except for the LZLJ-2019 vintage where both (R) and (S)-1,2-PG were present, all other samples only existed (R)-form, and a decreasing trend of (R)-enantiomer with aging time was observed. The enantiomeric ratio of 1,2-PG might be one of the potential markers for adulteration control of Baijiu as industrial 1,2-PG usually presented in the racemic mixture. Sensory analysis revealed olfactory thresholds of 4.66 mg/L and 23.92 mg/L for the (R)- and (S)-configurations in pure water respectively. GC-O showed both enantiomers exhibited different aromatic nuances.

Chemoenzymatic Stereodivergent Synthesis of All the Possible Stereoisomers of the 2,3-Dimethylglyceric Acid Ethyl Ester

2,3-dihydroxy-2-methylbutyric acid, also known as 2,3-dimethylglyceric acid, constitutes the acyl and/or the alcoholic moiety of many bioactive natural esters. Herein, we describe a chemoenzymatic methodology which gives access to all the four possible stereoisomers of the 2,3-dimethylglyceric acid ethyl ester. The racemic ethyl α-acetolactate, produced by the N-heterocycle carbene (NHC)-catalyzed coupling of ethyl pyruvate and methylacetoin was employed as the starting material. The racemic mixture was resolved through (S)-selective reductions, promoted by the acetylacetoin reductase (AAR) affording the resulting ethyl (2R,3S)-2,3-dimethylglycerate; the isolated remaining (S)-ethyl α-acetolactate was successively treated with baker’s yeast to obtain the corresponding (2S,3S) stereoisomer. syn-2,3-Dimethylgliceric acid ethyl ester afforded by reducing the rac-α-acetolactate with NaBH4 in the presence of ZnCl2 was kinetically resolved through selective acetylation with lipase B from Candida antarctica (CAL-B) and vinyl acetate to access to (2S,3R) stereoisomer. Finally, the (2R,3R) stereoisomer, was prepared by C3 epimerization of the (2R,3S) stereoisomer recovered from the above kinetic resolution, achieved through the TEMPO-mediated oxidation, followed by the reduction of the produced ketone with NaBH4. The resulting 2,3-dimethylglycertate enriched in the (2R,3R) stereoisomer was submitted to stereospecicific acetylation with vinyl acetate and CAL-B in order to separate the major stereoisomer. The entire procedure enabled conversion of the racemic α-acetolactate into the four enantiopure stereoisomers of the ethyl 2,3-dihydroxy-2-methylbutyrate with the following overall yields: 42% for the (2R,3S), 40% for the (2S,3S), 42% for the (2S,3R) and 20% for the (2R,3R).

Tracking the Source of Enantioselectivity

<p>Enantioselectivity remains one of synthetic chemistry’s most formidable problems. It arises due to the formation of diastereomeric species in a reaction, either in the form of diastereomeric intermediates or a set of diastereomeric transition states. Without control a racemic mixture is formed. A resolution method is then required to separate the enantiomers. Any given resolution method will rely on the differing energies of diastereomers to allow for their separation. Experimentally there are a myriad of different options that may be used to induce separation; for example chromatography and/or crystallisation. The actual process that occurs through- out this separation has not, however, been fully investigated in all cases. A better understanding of the process is able to provide an understanding of how resolution methods work i.e. when diastereomers occur and how great their energy differences are. This is vital in increasing the efficiency and effectiveness of any given resolution method. This theoretical study completed an investigation of the reaction pathway between the enantiomers of 2-formyl-3-hydroxyl[2.2]paracyclophane (FHPC) with (S)-valyl-(S)-valine. A subsequent investigation of an alternative resolution method, involving (R)-α-PEAM, was also conducted. This latter resolution method was proposed experimentally as a simpler method that could aid in improving the separation of the enantiomers. This investigation was carried out using Density Functional Theory (DFT) with the PBE0 functional and the triple-ζ TZVP basis set. The complete reaction profile was determined and diastereomeric intermediates and transition states for both resolution methods along two different pathways were determined; the ‘N-deprotonation Pathway’ and the ‘O-deprotonation Pathway’. The inadequacy of the first resolution method was found to be due to the presence of copper(II). Furthermore it was discovered that the re- action for both pathways would most likely proceed through the ‘O-deprotonation Pathway’ due to the barriers being lower in energy.</p>

Tracking the Source of Enantioselectivity

<p>Enantioselectivity remains one of synthetic chemistry’s most formidable problems. It arises due to the formation of diastereomeric species in a reaction, either in the form of diastereomeric intermediates or a set of diastereomeric transition states. Without control a racemic mixture is formed. A resolution method is then required to separate the enantiomers. Any given resolution method will rely on the differing energies of diastereomers to allow for their separation. Experimentally there are a myriad of different options that may be used to induce separation; for example chromatography and/or crystallisation. The actual process that occurs through- out this separation has not, however, been fully investigated in all cases. A better understanding of the process is able to provide an understanding of how resolution methods work i.e. when diastereomers occur and how great their energy differences are. This is vital in increasing the efficiency and effectiveness of any given resolution method. This theoretical study completed an investigation of the reaction pathway between the enantiomers of 2-formyl-3-hydroxyl[2.2]paracyclophane (FHPC) with (S)-valyl-(S)-valine. A subsequent investigation of an alternative resolution method, involving (R)-α-PEAM, was also conducted. This latter resolution method was proposed experimentally as a simpler method that could aid in improving the separation of the enantiomers. This investigation was carried out using Density Functional Theory (DFT) with the PBE0 functional and the triple-ζ TZVP basis set. The complete reaction profile was determined and diastereomeric intermediates and transition states for both resolution methods along two different pathways were determined; the ‘N-deprotonation Pathway’ and the ‘O-deprotonation Pathway’. The inadequacy of the first resolution method was found to be due to the presence of copper(II). Furthermore it was discovered that the re- action for both pathways would most likely proceed through the ‘O-deprotonation Pathway’ due to the barriers being lower in energy.</p>

A prospective randomized clinical study to compare the efficacy of 0.25% bupivacaine with clonidine and 0.25% levobupivacaine with clonidine in supraclavicular brachial plexus block for upper limb surgeries

:Bupivacaine is an amide local anesthetic, available as a racemic mixture of Dextro and Levorotatory Isomers. Due to its rapid onset and longer duration of anesthesia, It is routinely preferred in various regional anesthetic techniques. However, it is associated with serious cardiovascular and neurological toxicity. Its pure S- enantiomer, Levobupivacaine having similar pharmacological profile is known to have lesser cardiovascular and CNS toxicity. Combining adjuvants like clonidine, a centrally acting partial alpha-2-adrenergic agonist to improve quality of anesthesia is common practice. Hence, the aim of our study is to compare efficacy and safety of 0.25% Levobupivacaine and 0.25% Bupivacaine when combined with clonidine in supraclavicular brachial plexus block for upper limb surgeries.Eighty patients aged between 18 to 60 years with ASA physical status I-II, scheduled for elective upper limb surgeries under were randomized into two groups. Peripheral nerve stimulator guided Supraclavicular brachial plexus block was administered. Group BC received 30ml of 0.25% Bupivacaine plus 1µg/kg Clonidine and Group LC 30ml of 0.25% Levobupivacaine plus 1µg/kg Clonidine. The time of onset of sensory and motor block, duration of sensory and motor block, perioperative hemodynamic parameters, postoperative pain for 24hours and adverse effects were studies.Group LC had faster onset of sensory block (p= 0.014) as well as faster onset of motor block (p= 0.012) compared to group BC. However, durations of sensory block and motor block were statistically not significant in both the groups (p&#62;0.05). Perioperative hemodynamic parameters and assessment of pain during 24 hours of post operative period were comparable and statistically not significant.1mcg/kg of clonidine used as an adjuvant to 30ml of 0.25% Levobupivacaine produces faster onset of sensory and motor block compared to 0.25% Bupivacaine in supraclavicular brachial plexus block. However, similar anesthetic efficacy in terms of duration of sensory and motor block, hemodynamics and postoperative analgesia were observed.

A Single Low Dose of Dexmedetomidine Efficiently Attenuates Esketamine-Induced Overactive Behaviors and Neuronal Hyperactivities in Mice

Introduction: Esketamine (Esk) (S(+)-ketamine) is now used as an alternative to its racemic mixture, i. e., ketamine in anesthesia. Esk demonstrated more powerful potency and rapid recovery in anesthesia and less psychotomimetic side effects comparing with ketamine, but Esk could still induce psychological side effects in patients. This study was to investigate whether dexmedetomidine (Dex) can attenuate the Esk-induced neuronal hyperactivities in Kunming mice.Methods: Dexmedetomidine 0.25, 0.5, and 1 mg/kg accompanied with Esk 50 mg/kg were administrated on Kunming mice to assess the anesthesia quality for 1 h. The indicators, such as time to action, duration of agitation, duration of ataxia, duration of loss pedal withdrawal reaction (PWR), duration of catalepsy, duration of righting reflex (RR) loss, duration of sedation, were recorded for 1 h after intraperitoneal administration. The c-Fos expression in the brain was detected by immunohistochemistry and Western Blot after 1 h of administration. Considering the length of recovery time for more than 1 h in Dex and Dex with Esk groups, other mice were repeatedly used to evaluate recovery time from the administration to emerge from anesthesia.Results: Dexmedetomidine dose-dependently increased recovery time when administrated with Esk or alone. Dex combined with Esk efficiently attenuated the duration of agitation, ataxia, and catalepsy. Dex synergically improved the anesthesia of Esk by increasing the duration of sedation, loss of RR, and loss of PWR. Esk induced the high expression of c-Fos in the cerebral cortex, hippocampus, thalamus, amygdala, hypothalamus, and cerebellum 1 h after administration. Western Blot results indicated that Dex at doses of 0.25, 0.5, and 1 mg/kg could significantly alleviate the Esk-induced c-Fos expression in the mice brain.Conclusion: Dexmedetomidine ranged from 0.25 to 1 mg/kg could improve the anesthesia quality and decreased the neuronal hyperactivities and the overactive behaviors when combined with Esk. However, Dex dose-dependently increased the recovery time from anesthesia. It demonstrated that a small dose of Dex 0.25 mg/kg could be sufficient to attenuate Esk-induced psychotomimetic side effects without extension of recovery time in Kunming mice.

Lipase Assisted (S)-Ketoprofen Resolution from Commercially Available Racemic Mixture

Ketoprofen is a commercially available drug sold as a racemic mixture that belongs to the family of non-steroidal anti-inflammatory drugs known as profens. It has been demonstrated (in vitro) that (S)-ketoprofen is around 160 times more potent than its enantiomer (R)-ketoprofen, while accumulation of (R)-ketoprofen can cause serious side effects, such as dyspepsia, gastrointestinal ulceration/bleeding, pain, salt and fluid retention, and hypertension. In this work, four commercially available lipases were systematically assessed. Parameters such as conversion, enantiomeric excess, and enantioselectivity were considered. Among them, and by evaluating lipase load, temperature, solvent, and alcohol, Candida rugosa lipase exhibited the best results in terms of enantioselectivity E = 185 ((S)-enantiopreference) with esterification conversions of c = 47% (out of 50%) and enantiomeric excess of 99%. The unreacted (R)-enantiomer was recovered by liquid-liquid extraction and racemized under basic media, which was recycled as starting material. Finally, the (S)-alkyl ketoprofen ester was successfully enzymatically hydrolyzed to the desired (S)-ketoprofen with c = 98.5% and 99% ee. This work demonstrated the benefit and efficiency of using Candida rugosa lipase to kinetically resolve racemic ketoprofen by an environmentally friendly protocol and with the recycling of the undesired (R)-ketoprofen.