Over the past two decades, the domains of both frontline synthetic organic chemistry and process chemistry have seen an increase in crosstalk between asymmetric organic/organometallic approaches and ...enzymatic approaches to stereocontrolled synthesis. This review highlights the particularly auspicious role for dehydrogenase enzymes in this endeavor, with a focus on dynamic reductive kinetic resolutions (DYRKR) to “deracemize” building blocks, often setting two stereocenters in so doing. The scope and limitations of such dehydrogenase‐mediated processes are overviewed, as are future possibilities for the evolution of enzymatic DYRKR.
A formal synthesis of the antiviral drug (-)-oseltamivir (Tamiflu) has been accomplished starting from
-anisic acid via a dissolving metal or electrochemical Birch reduction. The correct absolute ...stereochemistry is efficiently set through enzyme-catalyzed carbonyl reduction on the resultant racemic α,β-unsaturated ketone. A screen of a broad ketoreductase (KRED) library identified several that deliver the desired allylic alcohol with nearly perfect facial selectivity at the new center for each antipodal substrate, indicating that the enzyme also is able to completely override inherent diastereomeric bias in the substrate. Conversion is complete, with d-glucose serving as the terminal hydride donor (glucose dehydrogenase). For each resulting diastereomeric secondary alcohol, O/N-interconversion is then efficiently effected either by synfacial 3,3-sigmatropic allylic imidate rearrangement or by direct, stereoinverting N-Mitsunobu chemistry. Both stereochemical outcomes have been confirmed crystallographically. The α,β-unsaturation is then introduced via an α-phenylselenylation/oxidation/pyrolysis sequence to yield the targeted (
)-
-acyl-protected 5-amino-1,3-cyclohexadiene carboxylates, key advanced intermediates for oseltamivir pioneered by Corey (
-Boc) and Trost (
-phthalamido), respectively.
Recent political unrest has highlighted the importance of understanding the short- and long-term effects of gamma-radiation exposure on human health and survivability. In this regard, effective ...treatment for acute radiation syndrome (ARS) is a necessity in cases of nuclear disasters. Here, we propose 20 therapeutic targets for ARS identified using a systematic approach that integrates gene coexpression networks obtained under radiation treatment in humans and mice, drug databases, disease-gene association, radiation-induced differential gene expression, and literature mining. By selecting gene targets with existing drugs, we identified potential candidates for drug repurposing. Eight of these genes (BRD4, NFKBIA, CDKN1A, TFPI, MMP9, CBR1, ZAP70, IDH3B) were confirmed through literature to have shown radioprotective effect upon perturbation. This study provided a new perspective for the treatment of ARS using systems-level gene associations integrated with multiple biological information. The identified genes might provide high confidence drug target candidates for potential drug repurposing for ARS.
A convenient synthetic route to α,α-difluoroalkylphosphonates is described. Structurally diverse aldehydes are condensed with LiF2CP(O)(OCH2CHCH2)2. The resultant alcohols are captured as the ...pentafluorophenyl thionocarbonates and efficiently deoxygenated with HSnBu3, BEt3, and O2, and then smoothly deblocked with CpRu(IV)(π-allyl)quinoline-2-carboxylate (1–2 mol %) in methanol as an allyl cation scavenger. These mild deprotection conditions provide access to free α,α-difluoroalkylphosphonates in nearly quantitative yield. This methodology is used to rapidly construct new bis-α,α-difluoroalkyl phosphonate inhibitors of PTPIB (protein phosphotyrosine phosphatase-1B).
Transbronchial lung cryobiopsy is increasingly being used for the assessment of diffuse parenchymal lung diseases. Several studies have shown larger biopsy samples and higher yields compared with ...conventional transbronchial biopsies. However, the higher risk of bleeding and other complications has raised concerns for widespread use of this modality.
To study the diagnostic accuracy and safety profile of transbronchial lung cryobiopsy and compare with video-assisted thoracoscopic surgery (VATS) by reviewing available evidence from the literature.
Medline and PubMed were searched from inception until December 2016. Data on diagnostic performance were abstracted by constructing two-by-two contingency tables for each study. Data on a priori selected safety outcomes were collected. Risk of bias was assessed with the Quality Assessment of Diagnostic Accuracy Studies tool. Random effects meta-analyses were performed to obtain summary estimates of the diagnostic accuracy.
The pooled diagnostic yield, pooled sensitivity, and pooled specificity of transbronchial lung cryobiopsy were 83.7% (76.9-88.8%), 87% (85-89%), and 57% (40-73%), respectively. The pooled diagnostic yield, pooled sensitivity, and pooled specificity of VATS were 92.7% (87.6-95.8%), 91.0% (89-92%), and 58% (31-81%), respectively. The incidence of grade 2 (moderate to severe) endobronchial bleeding after transbronchial lung cryobiopsy and of post-procedural pneumothorax was 4.9% (2.2-10.7%) and 9.5% (5.9-14.9%), respectively.
Although the diagnostic test accuracy measures of transbronchial lung cryobiopsy lag behind those of VATS, with an acceptable safety profile and potential cost savings, the former could be considered as an alternative in the evaluation of patients with diffuse parenchymal lung diseases.
How changes in enzyme structure and dynamics facilitate passage along the reaction coordinate is a fundamental unanswered question. Here, we use time-resolved mix-and-inject serial crystallography ...(MISC) at an X-ray free electron laser (XFEL), ambient-temperature X-ray crystallography, computer simulations, and enzyme kinetics to characterize how covalent catalysis modulates isocyanide hydratase (ICH) conformational dynamics throughout its catalytic cycle. We visualize this previously hypothetical reaction mechanism, directly observing formation of a thioimidate covalent intermediate in ICH microcrystals during catalysis. ICH exhibits a concerted helical displacement upon active-site cysteine modification that is gated by changes in hydrogen bond strength between the cysteine thiolate and the backbone amide of the highly strained Ile152 residue. These catalysis-activated motions permit water entry into the ICH active site for intermediate hydrolysis. Mutations at a Gly residue (Gly150) that modulate helical mobility reduce ICH catalytic turnover and alter its pre-steady-state kinetic behavior, establishing that helical mobility is important for ICH catalytic efficiency. These results demonstrate that MISC can capture otherwise elusive aspects of enzyme mechanism and dynamics in microcrystalline samples, resolving long-standing questions about the connection between nonequilibrium protein motions and enzyme catalysis.
Described is an efficient stereocontrolled route into valuable, densely functionalized fluorinated phosphonates that takes advantage of (i) a Clostridial enzyme to set the absolute stereochemistry ...and (ii) a new 3,3-sigmatropic rearrangement of the thiono-Claisen variety that is among the fastest sigmatropic rearrangements yet reported. Here, a pronounced rate enhancement is achieved by distal fluorination. This rearrangement is completely stereoretentive, parlaying the enzymatically established β-C–O stereochemistry in the substrate into the δ-C–S stereochemistry in the product. The final products are of interest to chemical biology, with a platform for Zn-aminopeptidase A inhibitors being constructed here. The enzyme, Clostridium acetobutylicum (CaADH), recently expressed by our group, reduces a spectrum of γ,δ-unsaturated β-keto-α,α-difluorophosphonate esters (93–99% ee; 10 examples). The resultant β-hydroxy-α,α-difluorophosphonates possess the “l”-stereochemistry, opposite to that previously observed for the CaADH-reduction of ω-keto carboxylate esters (“d”), indicating an unusual active site plasticity. For the thiono-Claisen rearrangement, a notable structure–reactivity relationship is observed. Measured rate constants vary by over 3 orders of magnitude, depending upon thiono-ester structure. Temperature-dependent kinetics reveal an unusually favorable entropy of activation (ΔS ‡ = 14.5 ± 0.6 e.u.). Most notably, a 400-fold rate enhancement is seen upon fluorination of the distal arene ring, arising from favorable enthalpic (ΔΔH ‡ = −2.3 kcal/mol) and entropic (ΔΔS ‡ = 4 e.u., i.e. 1.2 kcal/mol at rt) contributions. The unusual active site plasticity seen here is expected to drive structural biology studies on CaADH, while the exceptionally facile sigmatropic rearrangement is expected to drive computational studies to elucidate its underlying entropic and enthalpic basis.
Pleuroscopy, also known as medical thoracoscopy, is a minimally invasive procedure to inspect and perform a biopsy of the pleural space as well as to perform therapeutic interventions. It differs ...from conventional video-assisted thoracic surgery in that it may be performed under moderate sedation in the endoscopy suite without the need for intubation or single-lung ventilation. The diagnostic accuracy of this procedure approaches 100% in malignant and tuberculous pleural effusions. Complication rates are low (2%-5%) and are typically minor (subcutaneous emphysema, bleeding, infection), with mortality rates <0.1%. Therapeutic interventions, such as chemical pleurodesis, may be performed during pleuroscopy for recurrent, symptomatic malignant pleural effusions, with success rates approaching 90%. In trained hands, pleuroscopy is a safe and well-tolerated procedure with high diagnostic accuracy and therapeutic efficacy.
Developing specific chemical functionalities to deploy in biological environments for targeted enzyme inactivation lies at the heart of mechanism-based inhibitor development but also is central to ...other protein-tagging methods in modern chemical biology including activity-based protein profiling and proteolysis-targeting chimeras. We describe here a previously unknown class of potential PLP enzyme inactivators; namely, a family of quaternary, α-(1′-fluoro)vinyl amino acids, bearing the side chains of the cognate amino acids. These are obtained by the capture of suitably protected amino acid enolates with β,β-difluorovinyl phenyl sulfone, a new (1′-fluoro)vinyl cation equivalent, and an electrophile that previously eluded synthesis, capture and characterization. A significant variety of biologically relevant AA side chains are tolerated including those for alanine, valine, leucine, methionine, lysine, phenylalanine, tyrosine, and tryptophan. Following addition/elimination, the resulting transoid α-(1′-fluoro)-β-(phenylsulfonyl)vinyl AA-esters undergo smooth sulfone–stannane interchange to stereoselectively give the corresponding transoid α-(1′-fluoro)-β-(tributylstannyl)vinyl AA-esters. Protodestannylation and global deprotection then yield these sterically encumbered and densely functionalized quaternary amino acids. The α-(1′-fluoro)vinyl trigger, a potential allene-generating functionality originally proposed by Abeles, is now available in a quaternary AA context for the first time. In an initial test of this new inhibitor class, α-(1′-fluoro)vinyllysine is seen to act as a time-dependent, irreversible inactivator of lysine decarboxylase from Hafnia alvei. The enantiomers of the inhibitor could be resolved, and each is seen to give time-dependent inactivation with this enzyme. Kitz–Wilson analysis reveals similar inactivation parameters for the two antipodes, L-α-(1′-fluoro)vinyllysine (K i = 630 ± 20 μM; t 1/2 = 2.8 min) and D-α-(1′-fluoro)vinyllysine (K i = 470 ± 30 μM; t 1/2 = 3.6 min). The stage is now set for exploration of the efficacy of this trigger in other PLP-enzyme active sites.
To avoid reexpansion pulmonary edema (RPE), thoracenteses are often limited to draining no more than 1 L. There are, however, significant clinical benefits to removing more than 1 L of fluid. The ...purpose of this study was to define the incidence of RPE among patients undergoing large-volume (> or = 1 L) thoracentesis.
One hundred eighty-five patients undergoing large-volume thoracentesis were included in this study. The volume of fluid removed, absolute pleural pressure, pleural elastance, and symptoms during thoracentesis were compared in patients who did and did not experience RPE.
Of the 185 patients, 98 (53%) had between 1 L and 1.5 L withdrawn, 40 (22%) had between 1.5 L and 2 L withdrawn, 38 (20%) had between 2 L and 3 L withdrawn, and 9 (5%) had more than 3 L withdrawn. Only 1 patient (0.5%, 95% confidence interval: 0.01% to 3%) experienced clinical RPE. Four patients (2.2%, 95% confidence interval: 0.06% to 5.4%) had radiographic RPE (diagnosed only on postprocedure imaging without clinical symptoms). The incidence of RPE was not associated with the absolute change in pleural pressure, pleural elastance, or symptoms during thoracentesis.
Clinical and radiographic RPE after large-volume thoracentesis is rare and independent of the volume of fluid removed, pleural pressures, and pleural elastance. The recommendation to terminate thoracentesis after removing 1 L of fluid needs to be reconsidered: large effusions can, and should, be drained completely as long as chest discomfort or end-expiratory pleural pressure less than -20 cm H2O does not develop.
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