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Major Fragments (major + fragment)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

Studies Directed Towards the Total Synthesis of (,)-Dictyostatin

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2010
Jhillu S. Yadav
Abstract The stereoselective synthesis of the three major fragments (C1,C9, C10,C17, and C19,C26) of an antimitotic marine macrolide, (,)-dictyostatin, has been achieved with a desymmetrization strategy and Oppolzer syn and anti aldol protocols as the key reactions. Takai olefination and Sonogashira coupling reactions were successfully utilized to establish the 2Z,4E -dienoate portion of the C1,C9 fragment and Stille coupling for the Z -diene core of C19,C26. [source]

Photoionization studies on various quinones by an infrared laser desorption/tunable VUV photoionization TOF mass spectrometry

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2008
Yang Pan
Abstract Photoionization and dissociative photoionization characters of six quinones, including 1,2-naphthoquinone (1,2-NQ), 1,4-naphthoquinone (1,4-NQ), 9,10-phenanthroquinone (PQ), 9,10-anthraquinone (AQ), benz[a]- anthracene-7,12-dione (BAD) and 1,2-acenaphthylenedione (AND) have been studied with an infrared laser desorption/tunable synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (IR LD/VUV PIMS) technique. Mass spectra of these compounds are obtained at different VUV photon energies. Consecutive losses of two carbon monoxide (CO) groups are found to be the main fragmentation pathways for all the quinones. Detailed dissociation processes are discussed with the help of ab initio B3LYP calculations. Ionization energies (IEs) of these quinones and appearance energies (AEs) of major fragments are obtained by measuring the photoionization efficiency (PIE) spectra. The experimental results are in good agreement with the theoretical data. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Detection of Coconut cadang-cadang viroid sequences in oil and coconut palm by ribonuclease protection assay

ANNALS OF APPLIED BIOLOGY, Issue 1 2009
G. Vadamalai
Abstract A ribonuclease protection assay (RPA) has been developed for detecting Coconut cadang-cadang viroid (CCCVd) sequences. An RNA probe complementary to full-length CCCVd246 was used, terminating at nucleotide 65 in the upper conserved region, and linked to a non-viroid 5, sequence, which acted as an internal control for ribonuclease activity. Extracts from CCCVd-infected coconut (Cocos nucifera) and African oil (Elaeis guineensis) palms protected three major fragments of approximately 250, 125 and 50 nt and a variable number of minor fragments. Extracts of healthy coconut palms, Potato spindle tuber viroid -infected tomato and transfer RNA did not protect the probe. The approximately 250 nt fragment is predicted to indicate the presence of monomers and dimers of circular CCCVd246, linear CCCVd246 with the same termini as the probe and point mutants of these forms. The origin of smaller protected fragments is discussed. RPA-detected CCCVd sequences in 13 of 18 oil palms surveyed in a commercial plantation in Malaysia. Signal intensity varied between the positive oil palms and was generally lower than in coconut palms infected with CCCVd. An infection phenotype was implied but not confirmed by the observation that in a group of 10 oil palms with orange leaf spotting, 9 contained CCCVd, whereas in a group of 8 palms without orange spotting, the viroid was detected in 4. Of four coconut palms in Sri Lanka shown by dot-blot assay to contain CCCVd-related RNA, one was shown by RPA to be positive for the CCCVd246 sequence. RPA is therefore a robust and sensitive test for CCCVd sequences, and our results show that sequences closely related to CCCVd246 are not confined to the Philippines. [source]

Stereoselective Synthesis of (,)-Amphidinolide,E

CHEMISTRY - AN ASIAN JOURNAL, Issue 8-9 2008
Hyuk Kim
Abstract The total synthesis of (,)-amphidinolide,E was accomplished by following a synthetic scheme that incorporates the labile C2 stereocenter at a very late stage. The oxolane unit was prepared by ,-alkoxyacrylate radical cyclization. The enyne metathesis reaction was employed for the synthesis of the side chain. The Kocienski,Julia reaction was used for the union of the two major fragments, and the Kita macrolactonization protocol was used for macrolide synthesis. [source]