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RISS 인기검색어
- 검색키워드
- 저자 : Rita Pal (검색결과 3 건)
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Synthesis of SSEA-1, SSEA-3 and SSEA-4 for developing bio-compatible-nanomaterials
Rita Pal,Naoko Komura,Akihiro Imamura,Hiromune Ando,Hideharu Ishida,Makoto Kiso 한국당과학회 2012 한국당과학회 학술대회 Vol.2012 No.1
Stage-specific embryonic antigens1 (SSEA’s) have been identified as glycosphingolipids which play diverse roles in embryonic development, such as regulation of cell growth, recognition and differentiation. It’s well-documented that human ES and iPS cell express predominantly glycosphingolipids of the globo- series2 such as SSEA-3 and SSEA-4, which are also hallmarks of human embryonal carcinoma cells. While, SSEA-1 represents a marker for murine pluripotent stem cells, in which it plays an important role in adhesion and migration of the cells in the preimplantation embryo. We are intended to integrate their biological functions into biocompatible nanomaterials for developing ES and iPS cell culturing system. To conjugate with nanomaterials these molecules have been suitably functionalized at the terminal position. In the present study, a convergent chemical synthesis of SSEA-1 SSEA-3 and SSEA-4 will be discussed.
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Ju Yuel Baek,Bo-Young Lee,Rita Pal,Mi Young Kim,Kwan Soo Kim 한국당과학회 2010 한국당과학회 학술대회 Vol.2010 No.1
Development of efficient and stereoselective glycosylation methodologies has been a major concern in synthetic organic chemistry over the past decade due to important roles of complex oligosaccharides in many fundamental life-sustaining processes. The selection of an appropriate glycosyl donor is one of the key processes for the successful glycosylation in terms of efficiency and stereoselectivity. We reported previously a new direct glycosylation method with anomeric hydroxy sugars as donors and phthalic anhydride and triflic anhydride as promoters, and the result of investigation of intermediates in the new glycosylation by low temperature NMR [1]. Although our direct glycosylation method works nicely in various glycosylations including stereoselective β-mannosylations, in certain cases, it gives undesired self-condensed esters of donors. In the first part of the lecture is presented a modified, improved method for the direct glycosylation with anomeric hydroxy sugars by employing phthalic anhydride derivatives in the place of phthalic anhydride itself. One of the most useful stereoselective glycosylation strategy utilizing protecting groups has been the 1,2-trans glycoside synthesis. Although the acyl groups at O-2 of donors give 1,2-trans glycosides by the neighboring group participation, their electron-withdrawing effects on the glycosylation stereochemistry might not have been properly recognized because of the overwhelming effect of the neighboring group participation. In fact, the effect of the non-participating electron-withdrawing groups such as methanesulfonyl and benzylsulfonyl groups at the O-2 positions of the donors on the glycosylation stereochemistry has been observed. Remote electron-withdrawing groups at O-3, O-4, and O-6 positions of pyranosyl donors or at O-3 and O-5 positions of furanosyl donors, which would reduce the reactivity of glycosyl donors, might also exert directing effects on the outcome of the stereochemistry of glycosylations. In fact, we reported previously that mannosylations of various acceptors with donors possessing an electron-withdrawing sulfonyl or acyl groups at O-3, O-4, or O-6 positions were found to be β-selective except when donors had 3-O-acyl and 6-O-acetyl groups, which afforded α-mannosides as major products [2]. The α-directing effect of 3-O-acyl and 6-O-acetyl groups was attributed to their remote participations while the origin of the β-directing effect was ascribed to the SN2-like reaction of the acceptor and the α-triflate intermediate, which is stabilized by remote electron-withdrawing groups. In the second part of the lecture is concerned with the directing effect of electron-withdrawing groups at the remote positions of donors on the stereochemistry in not only mannosylations but also other glycosylations. Directing effect of remote electron-withdrawing groups of other glycosyl donors was found to be quite different from the directing effect of those of mannosyl donors.
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COMMON FIXED POINT RESULTS UNDER C-DISTANCE IN TVS-CONE METRIC SPACES
A. K. Dubey,Urmila Mishra,Rita Pal 경남대학교 수학교육과 2018 Nonlinear Functional Analysis and Applications Vol.23 No.3
In 2011, Wang and Guo introduced the c-distance in a cone metric spaces and proved common fixed point results. The purpose of this paper is to extend and generalize some common fixed point results in literature for c-distance in tvs-cone metric spaces (with the underlying cone which is not normal) by replacing the constants in contractive conditions with functions.
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