76 research outputs found

    Iminohydantoin Lesion Induced in DNA by Peracids and Other Epoxidizing Oxidants

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    The oxidation of guanine to 5-carboxamido-5-formamido-2-iminohydantoin (2-Ih) is shown to be a major transformation in the oxidation of the single-stranded DNA 5-mer d(TTGTT) by m-CPBA and DMDO as a model for peracid oxidants and in the oxidation of the 5-base pair duplex d[(TTGTT)·(AACAA)] with DMDO. 2-Ih has not been reported as an oxidative lesion at the level of single/double-stranded DNA or at the nucleoside/nucleotide level. The lesion is stable to DNA digestion and chromatographic purification suggesting that 2-Ih may be a stable biomarker in vivo. The oxidation products have been structurally characterized and the reaction mechanism probed by oxidation of the monomeric species dGuo, dGMP and dGTP. DMDO selectively oxidizes the guanine moiety of dGuo, dGMP and dGTP to 2-Ih, and both peracetic and m-chloroperbenzoic acids exhibit the same selectivity. The presence of the glycosidic bond results in the stereoselective induction of an asymmetric center at the spiro carbon to give a mixture of diastereomers, with each diastereomer in equilibrium with a minor conformer through rotation about the formamido C-N bond. Labeling studies with 18O2-m-CPBA and H218O to determine the source of the added oxygen atoms have established initial epoxidation of the guanine 4-5 bond with pyrimidine ring contraction by an acyl 1,2-migration of guanine carbonyl C6 to form a transient dehydrodeoxyspiroiminodihydantoin followed by hydrolytic ring opening of the imidazolone ring. Consistent with the proposed mechanism, no 8-oxoguanine was detected as a product of the oxidations of the oligonucleotides or monomeric species mediated by DMDO or the peracids. The 2-Ih base thus appears to be a pathway-specific lesion generated by peracids and possibly other epoxidizing agents and holds promise as a potential biomarker

    Studies in terpenoids.48. Synthesis of 8-methoxycalamenene, a sesquiterpene of marine origin

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    Revision of the structure assigned to a monoterpene isolated from

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    Unambiguous synthesis of 2-methyl-3-isopropenylanisole (Image ) and 2-isopropenyl-3-methylanisole (Image ) has led to revision, from (Image ) to (Image ), of the structure assigned to a monoterpene phenol ether isolated fro

    Studies in terpenoids. Part LXXVI. Synthesis of (+)-(S)-ar-pseudotsugonal

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    pRC6H4CHMeCH2COCH2CHMe2p-RC_6H_4CHMeCH_2COCH_2CHMe_2 (I; R=CHO) was prepared from chiral I CR=Me) by oxidation to I (R=CO2H)(R=CO_2H), reduction to I (R=CH2OH)(R=CH_2OH), and oxidation to I (R=CHO)

    One-pot synthesis of nidorellaurenal and its one-step conversion to methyl nidorellaurinate, a constituent of Nidorella auriculata

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    Nidorellaurenal (4) is obtained in a one-pot reaction, involving heating of the known carbinol (8) with selenium dioxide in dimethyl sulphoxide. Conversion of 4 to methyl nidorellaurinate (6), the natural product from Nidorella auriculata, has been achieved by Corey's one-step procedure

    A novel sentiment aware dictionary for multi-domain sentiment classification

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    Sentiment Analysis is a sub area of Natural Language Processing (NLP) which extracts user's opinion and classifies it according to its polarity. This task has many applications but it is domain dependent and a costly task to annotate the corpora in every possible domain of interest before training the classifier. We are making an attempt to solve this problem by creating a sentiment aware dictionary using multiple domain data. This dictionary is created using labeled data from the source domain and unlabeled data from both source and target domains. Next, this dictionary is used to classify the unlabeled reviews of the target domain. The work is carried out in Hindi, the official language of India. The web pages in Hindi language is booming after the introduction of UTF-8 encoding style. When compared with labeling done by Hindi Sentiwordnet (HSWN), a general lexicon for word polarity, the proposed method is able to label 23-24 more number of words of target domain. The labels assigned by our method and the labels given by HSWN, for the available words, are compared and found matching with 76 accuracy. © 2017 Elsevier Ltd
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