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Now showing items 1 - 16 of 24

  • Evaluation of the effect of glycosylation on the enzymic hydrolysis of peptides

    Mehta, Seema   Meldal, Morten   Duus, Jens ?.   Bock, Klaus  

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  • Beneficial Participation of the Polymer: Improvement in Polymer-Supported Oligosaccharide Synthesis

    Mehta, Seema   Whitfield, Dennis  

    The reagent combination scandium(III) trifluoromethanesulfonate and acetic anhydride efficiently cleaves oligosaccharides bound to the polyethylene glycol (PEG) polymer-support via the dioxyxylene (DOX) linker. Unexpectedly, the site of cleavage is between the DOX linker and the PEG polymer. This method of cleavage allows for the use of DOX as a linker for synthesis on polystyrene-polyethylene glycol, PS-PEG beads.
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  • Ready Access to Sialylated Oligosaccharide Donors

    Mehta, Seema   Gilbert, Michel   Wakarchuk, Warren W.   Whitfield, Dennis M.  

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  • M1011 Epidemiology of Pediatric Gallbladder Disease: Retrospective Analysis of 406 Consecutive Cholecystectomies

    Mehta, Seema   Lopez, Monica E.   Chumpitazi, Bruno P.   Brandt, Mary L.   Fishman, Douglas S.  

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  • Novel Hetero-analogs of Methyl Maltoside Containing Sulfur and Selenium as Potential Glycosidase Inhibitors

    Mehta, Seema   Andrews, John S.   Johnston, Blair D.   Pinto, B. Mario  

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  • Book Review Myeloma Edited by Jayesh Mehta and Seema Singhal. 539 pp., illustrated. London, Martin Dunitz, 2002. $150. 1-901865-50-9

    Bladé   Joan  

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  • SEEMA MEHTA

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  • Tris(4-bromophenyl)aminium hexachloroantimonate-mediated glycosylations of selenoglycosides and thioglycosides. Evidence for single electron transfer?

    Mehta, Seema   Pinto, B. Mario  

    Radical cation-initiated glycosylation reactions of phenyl selenoglycosides are described. Glycosylations of phenyl selenoglycosides effected by the single-electron-transfer (SET) reagent, tris(4-bromophenyl)aminium hexachloroantimonate (BAHA), are examined with primary and secondary hydroxyl acceptors. The corresponding reaction of an ethyl thioglycoside with a primary hydroxyl acceptor is also examined. Reactions are performed in the presence of the SET quenching reagent, 1,2,4,5-tetramethoxybenzene, to assess whether BAHA-mediated glycosylation reactions involve SET. These experiments indicate that the reactions are completely quenched in dichloromethane but only partially in acetonitrile. The results provide support for the SET mechanism but an alternative mechanism involving electrophilic activation cannot be discounted. The oxidation potentials of various selenoglycosides are determined by cyclic voltammetry.
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  • Internally quenched fluorogenic, α-helical dimeric peptides and glycopeptides for the evaluation of the effect of glycosylation on the conformation of peptides

    Mehta, Seema   Meldal, Morten   Ferro, Vito   Duus, Jens ?.   Bock, Klaus  

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  • Polymer-Supported Synthesis of a Branched Trisaccharide of the Type IA Group B Streptococcus Capsular Polysaccharide: 3-Iodo-4-methoxybenzyl as a New O-Protecting Group

    Mehta, Seema   Whitfield, Dennis M.  

    The synthesis of a key branched trisaccharide (1), of the type IA Group B Streptococcus capsular polysaccharide is described. The monomethyl ether of polyethylene glycol (MeO–(CH2CH2O)n–H, MPEG) and dioxyxylene [p-(O)CH2–C6H4–CH2(O)–, DOX] have been used as the polymer-support/linker combination. Attempts to use the p-methoxybenzyl (PMB) protecting group under glycosylation conditions involving N-iodosuccinimide/silver trifuoromethanesulfonate promotion resulted in iodination to form the 3-iodo-4-methoxybenzyl (IPMB) derivative. Subsequently IPMB chloride was independently synthesized and used to introduce this new protecting group. The levulinoyl and the IPMB protecting groups have been used in an orthogonal manner to create 3,4-branching on a galactopyranosyl residue. Due to the enhanced acid stability of the IPMB group over the PMB group, the former group was critical to the success of the synthesis. The final trisaccharide and its intermediates were cleaved from the MPEG polymer-support by scandium(III)trifluoromethanesulfonate and acetic anhydride.
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  • Pneumocystis jirovecii prophylaxis in patients treated for high-grade gliomas:a survey among neuro-oncologists

    Skorupan, Nebojsa   Ranjan, Surabhi   Mehta, Seema   Yankulina, Olga   Nenortas, Nathan   Grossman, Stuart   Ye, Xiaobu   Holdhoff, Matthias  

    Background. Pneumocystis jirovecii pneumonia (PJP) is a known complication in patients with high-grade gliomas (HGGs) who are treated with radiation and chemotherapy. PJP prophylaxis is commonly recommended, but there are currently no clear guidelines regarding duration of treatment and choice of drugs. This study aimed to assess current practice patterns of PJP prophylaxis among neuro-oncologists. Methods. An online survey of 14 multiple choice questions was sent to 207 neuro-oncologists and medical oncologists treating brain cancers at all National Cancer Institute-designated cancer centers in the United States. Recipients were identified via a search of the cancer centers' websites. Results. Sixty-one invited experts completed the survey (response rate 29%; of these, 72% were neuro-oncologists, 18% were medical oncologists, and 10% were pediatric neuro-or medical oncologists). Seventy percent of respondents stated that they routinely prescribe PJP prophylaxis, while 7% do not provide prophylaxis. Eighty-one percent of respondents use absolute lymphocyte count (ALC) to assess lymphopenia and 13% also monitor CD4 lymphocyte counts during prophylaxis. The most commonly used first-line agent is trimethoprim-sulfamethoxazole (88% of respondents), followed by pentamidine (6%). Discontinuation of PJP prophylaxis is determined by the following: count recovery (33% by ALC; 18% by CD4 lymphocyte counts), radiation completion (23%), and chemotherapy completion (7%). Glucose-6-phosphate dehydrogenase levels were routinely checked by only 13% of respondents. Conclusions. PJP prophylaxis is commonly used in HGG patients, but there are large variations in practice patterns, including the duration of prophylaxis. As consideration for PJP prophylaxis affects all patients with HGG, standardization of prophylaxis should be formally addressed.
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  • Rapid Stool-Based Diagnosis of Clostridium difficile Infection by Real-Time PCR in a Children's Hospital

    Luna, Ruth Ann   Boyanton, Bobby L., Jr.   Mehta, Seema   Courtney, Ebony M.   Webb, C. Renee   Revell, Paula A.   Versalovic, James  

    Clostridium difficile is a major cause of nosocomial antibiotic-associated infectious diarrhea and pseudomembranous colitis. Detection of C. difficile by anaerobic bacterial culture and/or cytotoxicity assays has been largely replaced by rapid enzyme immunoassays (EIA). However, due to the lack of sensitivity of stool EIA, we developed a multiplex real-time PCR assay targeting the C. difficile toxin genes tcdA and tcdB. Stool samples from hospitalized pediatric patients suspected of having C. difficile-associated disease were prospectively cultured on cycloserine-cefoxitin-fructose agar following alcohol shock. Six testing modalities were evaluated, including stool EIA, culture EIA, and real-time PCR (tcdA and tcdB) of cultured isolates and stool samples. Real-time PCR detection was performed with tcdA and tcdB gene-specific primers and hydrolysis probes using the LightCycler platforms (Roche Diagnostics, Indianapolis, IN). A total of 157 samples from 96 pediatric patients were analyzed. The sensitivities of stool real-time PCR and stool EIA were 95% and 35%, respectively, with a specificity of 100% for both methods. The lower limit of detection of the stool real-time PCR was 30 CFU/ml of stool sample per reaction for tcdA and tcdB. This study highlights the poor performance of stool toxin EIAs in pediatric settings. Direct detection of C. difficile toxin genes in stool samples by real-time PCR showed sensitivity superior to that of stool and culture EIAs and performance comparable to that of real-time PCR assay of cultured isolates. Real-time PCR of DNA from stool samples is a rapid and cost-effective diagnostic modality for children that should facilitate appropriate patient management and halt the practice of serial testing by EIA.
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  • Resolution of Carbapenemase-Producing Klebsiella pneumoniae Outbreak in a Tertiary Cancer Center; the Role of Active Surveillance

    Rock, Clare   Curless, Melanie S.   Cantara, Maggie   Mehta, Seema   Marrone, Kristen A.   Carroll, Karen C.   Simner, Patricia   Maragakis, Lisa L.  

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  • Tris(4-bromophenyl)aminium hexachloroantimonate-mediated glycosylations of selenoglycosides and thioglycosides. Evidence for single electron transfer?

    Mehta, Seema   Pinto, B. Mario  

    Radical cation-initiated glycosylation reactions of phenyl selenoglycosides are described. Glycosylations of phenyl selenoglycosides effected by the single-electron-transfer (SET) reagent, tris(4-bromophenyl)aminium hexachloroantimonate (BAHA), are examined with primary and secondary hydroxyl acceptors. The corresponding reaction of an ethyl thioglycoside with a primary hydroxyl acceptor is also examined. Reactions are performed in the presence of the SET quenching reagent, 1,2,4,5-tetramethoxybenzene, to assess whether BAHA-mediated glycosylation reactions involve SET. These experiments indicate that the reactions are completely quenched in dichloromethane but only partially in acetonitrile. The results provide support for the SET mechanism but an alternative mechanism involving electrophilic activation cannot be discounted. The oxidation potentials of various selenoglycosides are determined by cyclic voltammetry.
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  • Disseminated sporotrichosis following iatrogenic immunosuppression for suspected pyoderma gangrenosum.

    White, Marissa   Adams, La'Tonzia   Phan, Casey   Erdag, Gulsun   Totten, Marissa   Lee, Richard   Lu, Xuelian   Mehta, Seema   Miller, Lloyd S   Zhang, Sean X  

    Sporotrichosis is an infection caused by the dimorphic fungus Sporothrix schenckii and related species that often arises from traumatic inoculation of inhabited soil and organic debris into skin. The infection is usually limited to the skin in immunocompetent patients, usually as lymphocutaneous sporotrichosis. Accurate diagnosis rests on clinical data and culture, and might be facilitated by biopsy identification of suppurative and granulomatous inflammation with fungal elements. In this Grand Round, we present a dramatic case of cutaneous sporotrichosis initially presented with an atypical large ulcer without associated lymphocutaneous spread, clinically mimicking pyoderma gangrenosum, and subsequently progressed to disseminated sporotrichosis in the setting of iatrogenic immunosuppression. We further review the clinical features, risk factors, and treatment of these disseminated sporotrichosis cases, and discuss the need for improved awareness of this fungus' potential link to cause disseminated and invasive fungal infections. Copyright =C2=A9 2019 Elsevier Ltd. All rights reserved.
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  • Extended spectrum beta-lactamase-producing Enterobacteriaceae infection in heart and lung transplant recipients and in mechanical circulatory support recipients.

    Bui, Kevin T   Mehta, Seema   Khuu, Tam H   Ross, David   Carlson, Margrit   Leibowitz, Matthew R   Schaenman, Joanna M   Saggar, Rajan   Lynch, Joseph P 3rd   Ardehali, Abbas   Kubak, Bernard M  

    BACKGROUND: Extended spectrum beta-lactamase (ESBL)-producing gram-negative bacilli are increasingly reported in patients with a variety of risk factors including prior cephalosporin and antibiotic usage, prolonged hospitalizations, existence of comorbid conditions, and critical illness.; METHODS: Retrospective review of infections caused by ESBL-producing Enterobacteriaceae was performed in heart transplant (HTx), lung transplant (LTx), and mechanical circulatory support (MCS) device recipients at a large transplant center.; RESULTS: Among 1065 patients transplanted/implanted, the incidence of ESBL-related infections (bacteremia, urinary tract infections, pneumonia, central venous catheter-associated infection, and wound infections) in HTx, LTx, and MCS device recipients was reported at 2.2%, 5.5%, and 10.7%, respectively, caused by ESBL-producing Klebsiella pneumoniae, Escherichia coli, Klebsiella oxytoca, and Citrobacter freundii.; CONCLUSIONS: Early detection and adequate duration of therapy for ESBL-producing Enterobacteriaceae in solid organ transplants and MCS device recipients are essential in successful patient outcomes including prevention of recurrent infection.=20
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