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Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) is used to characterize methylenedianiline (MDA) 3-ring and 4-ring species. Building on our previous MALDI-MS 2-ring MDA isomer study, here we compare 3-ring and 4-ring electrospray ionization (ESI) and MALDI results. In ESI, 3-ring and 4-ring MDAs each form a single [M + H] parent ion. However, in MALDI, each MDA multimer forms three unique precursor ions: [M + H], [M], and [M - H]. In this study, 3-ring and 4-ring MDA precursors are characterized to identify the unique fragment ions formed and their respective fragmentation pathways. In addition to the three possible precursors, the 3-ring and 4-ring species are higher-order oligomer precursors in polyurethane (PUR) production and thus provide additional insight into the polymeric behavior of these PUR hard block precursors. The combination of ion mobility-mass spectrometry (IM - MS) and tandem mass spectrometry (MS/MS) allow the structural characterization of these larger MDA multimers.
The cyclooxygenases COX-1 and COX-2 oxygenate arachidonic acid (AA) to prostaglandin H (PGH). COX-2 also oxygenates the endocannabinoids 2-arachidonoylglycerol (2-AG) and arachidonoylethanolamide (AEA) to the corresponding PGH analogs. Both enzymes are targets of nonsteroidal anti-inflammatory drugs (NSAIDs), but NSAID-mediated COX inhibition is associated with gastrointestinal toxicity. One potential strategy to counter this toxicity is to also inhibit fatty acid amide hydrolase (FAAH), which hydrolyzes bioactive fatty acid ethanolamides (FAEs) into fatty acids and ethanolamine. Here, we investigated the mechanism of COX inhibition by ARN2508, an NSAID that inhibits both COXs and FAAH with high potency, target selectivity, and decreased gastrointestinal toxicity in mouse models, presumably due to its ability to increase levels of FAEs. A 2.27-Å-resolution X-ray crystal structure of the COX-2·()-ARN2508 complex reveals that ARN2508 adopts a binding pose similar to that of its parent NSAID flurbiprofen. However, ARN2508's alkyl tail is inserted deep into the top channel, an active site region not exploited by any previously reported NSAID. As for flurbiprofen, ARN2508's potency is highly dependent on the configuration of the α-methyl group. Thus, ()-ARN2508 is more potent than ()-ARN2508 for inhibition of AA oxygenation by both COXs and 2-AG oxygenation by COX-2. Also, similarly to ()-flurbiprofen, ()-ARN2508 exhibits substrate selectivity for inhibition of 2-AG oxygenation. Site-directed mutagenesis confirms the importance of insertion of the alkyl tail into the top channel for ()-ARN2508's potency and suggests a role for Ser-530 as a determinant of the inhibitor's slow rate of inhibition compared with that of ()-flurbiprofen.
The absolute configuration (AC) of an axially chiral sulfonate (aCSO), 3,5-dimethyl-2-(naphthalen-1-yl)-6-(naphthalen-1-yl)benzenesulfonate (labeled as aCSO5), was investigated using optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) spectroscopies. All three methods led to the same conclusion and the AC of aCSO5 is reliably determined to be (-)-(aR, aR), or conversely (+)-(aS, aS).
© 2017 Wiley Periodicals, Inc.
Characterization of methylenedianiline (MDA) 2-ring isomers (2,2'-, 2,4'-, and 4,4'-MDA) is reported using matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS), a common technique used for characterizing synthetic polymers. MDA is a precursor to methylene diphenyl diisocyanate (MDI), a hard block component in polyurethane (PUR) synthesis. This work focuses on comparing MALDI results to those of our previous electrospray ionization-mass spectrometry (ESI-MS) studies. In ESI, 2-ring MDA isomers formed single unique [M + H] (199 Da) parent ions, whereas in MALDI each isomer shows significant formation of three precursor ions: [M - H] = 197 Da, [M] = 198 Da, and [M + H] = 199 Da. Structures and schemes are proposed for the MALDI fragment ions associated with each precursor ion. Ion mobility-mass spectrometry (IM-MS), tandem mass spectrometry (MS/MS), and computational methods were all critical in determining the structures for both precursor and fragment ions as well as the fragmentation mechanisms. The present study indicates that the [M - H] and [M] ions are formed by the MALDI process, explaining why they were not observed with ESI.
Recently, zebrafish and human cytochrome P450 (P450) 27C1 enzymes have been shown to be retinoid 3,4-desaturases. The enzyme is unusual among mammalian P450s in that the predominant oxidation is a desaturation and in that hydroxylation represents only a minor pathway. We show by proteomic analysis that P450 27C1 is localized to human skin, with two proteins of different sizes present, one being a cleavage product of the full-length form. P450 27C1 oxidized all--retinol to 3,4-dehydroretinol, 4-hydroxy (OH) retinol, and 3-OH retinol in a 100:3:2 ratio. Neither 3-OH nor 4-OH retinol was an intermediate in desaturation. No kinetic burst was observed in the steady state; neither the rate of substrate binding nor product release was rate-limiting. Ferric P450 27C1 reduction by adrenodoxin was 3-fold faster in the presence of the substrate and was ∼5-fold faster than the overall turnover. Kinetic isotope effects of 1.5-2.3 (on / ) were observed with 3,3-, 4,4-, and 3,3,4,4-deuterated retinol. Deuteration at C-4 produced a 4-fold increase in 3-hydroxylation due to metabolic switching, with no observable effect on 4-hydroxylation. Deuteration at C-3 produced a strong kinetic isotope effect for 3-hydroxylation but not 4-hydroxylation. Analysis of the products of deuterated retinol showed a lack of scrambling of a putative allylic radical at C-3 and C-4. We conclude that the most likely catalytic mechanism begins with abstraction of a hydrogen atom from C-4 (or possibly C-3) initiating the desaturation pathway, followed by a sequential abstraction of a hydrogen atom or proton-coupled electron transfer. Adrenodoxin reduction and hydrogen abstraction both contribute to rate limitation.
© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
Cytochrome P450 (P450, CYP) 17A1 plays a critical role in steroid metabolism, catalyzing both the 17α-hydroxylation of pregnenolone and progesterone and the subsequent 17α,20-lyase reactions to form dehydroepiandrosterone (DHEA) and androstenedione (Andro), respectively, critical for generating glucocorticoids and androgens. Human P450 17A1 reaction rates examined are enhanced by the accessory protein cytochrome (), but the exact role of in P450 17A1-catalyzed reactions is unclear as are several details of these reactions. Here, we examined in detail the processivity of the 17α-hydroxylation and lyase steps. did not enhance reaction rates by decreasing the rates of any of the steroids. Steroid binding to P450 17A1 was more complex than a simple two-state system. Pre-steady-state experiments indicated lag phases for Andro production from progesterone and for DHEA from pregnenolone, indicating a distributive character of the enzyme. However, we observed processivity in pregnenolone/DHEA pulse-chase experiments. ()-Orteronel was three times more inhibitory toward the conversion of 17α-hydroxypregnenolone to DHEA than toward the 17α-hydroxylation of pregnenolone. IC values for ()-orteronel were identical for blocking DHEA formation from pregnenolone and for 17α-hydroxylation, suggestive of processivity. Global kinetic modeling helped assign sets of rate constants for individual or groups of reactions, indicating that human P450 17A1 is an inherently distributive enzyme but that some processivity is present, some of the 17α-OH pregnenolone formed from pregnenolone did not dissociate from P450 17A1 before conversion to DHEA. Our results also suggest multiple conformations of P450 17A1, as previously proposed on the basis of NMR spectroscopy and X-ray crystallography.
© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
The first natural occurrence in optically active form of the dimeric flavonoid agathisflavone and definition of its axial chirality using chiroptical spectroscopic methods are described. The experimental electronic circular dichroism, electronic dissymmetry factor, optical rotatory dispersion, vibrational circular dichroism (VCD), and vibrational dissymmetry factor spectra of agathisflavone are presented and analyzed with their corresponding quantum chemical predictions to definitively assign the axial chirality of (-)-agathisflavone as (aS).
Chiroptical spectroscopy has evolved into a promising tool for chiral molecular structural determination in the last four decades. Determination of the absolute configurations (ACs) of bromochlorofluoromethane and [(2) H1 ,(2) H2 ,(2) H3 ]-neopentane demonstrated the enviable advantages of chiroptical spectroscopy. Furthermore, uncovering the errors in the ACs reported in the literature established a glimpse of what can be accomplished with the modern chiroptical spectroscopic methods. Despite these triumphs, it is important to exercise caution in the practice of chiroptical spectroscopic methods, because certain widely practiced approaches can lead to erroneous conclusions. Selected major accomplishments and special precautions needed for future applications are emphasized. Chirality 28:445-452, 2016. © 2016 Wiley Periodicals, Inc.
© 2016 Wiley Periodicals, Inc.
(-)-Centratherin is a bioactive sesquiterpenoid lactone, whose absolute configuration (AC) was not established, but has been proposed based on those of germacrane precursors. To verify this proposal, the experimental electronic circular dichroism (ECD), electronic dissymmetry factor (EDF), optical rotatory dispersion (ORD), vibrational circular dichroism (VCD), and vibrational dissymmetry factor (VDF) spectra of (-)-centratherin have been analyzed with the corresponding density functional theoretical predictions. These analyses suggest the AC of naturally occurring (-)-centratherin to be (6R,7R,8S,10R,2'Z).
This Letter describes the lead optimization of the VU0486321 series of mGlu1 positive allosteric modulators (PAMs). While first generation PAMs from Roche were reported in the late 1990s, little effort has focused on the development of mGlu1 PAMs since. New genetic data linking loss-of-function mutant mGlu1 receptors to schizophrenia, bipolar disorder and other neuropsychiatric disorders has rekindled interest in the target, but the ideal in vivo probe, for example, with good PK, brain penetration and low plasma protein binding, for robust target validation has been lacking. Here we describe the first modifications to the central aryl core of the VU0486321 series, where robust SAR was noted. Moreover, structural variants were identified that imparted selectivity (up to >793-fold) versus mGlu4.
Copyright © 2015 Elsevier Ltd. All rights reserved.