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991.
992.
Air-stable, storable, and highly efficient chiral zirconium catalysts for enantioselective Mannich-type, aza Diels-Alder, aldol, and hetero Diels-Alder reactions 下载免费PDF全文
Kobayashi S Ueno M Saito S Mizuki Y Ishitani H Yamashita Y 《Proceedings of the National Academy of Sciences of the United States of America》2004,101(15):5476-5481
For the synthesis of optically active compounds, chiral catalysts have attracted much attention because large quantities of optically active molecules can be prepared from a small amount of a chiral source. However, many chiral catalysts are often unstable in air (oxygen) and/or in the presence of water. This is especially the case in chiral Lewis acid catalysis, because most Lewis acids are air- and moisture-sensitive. Therefore, many catalysts are prepared in situ in an appropriate solvent just before use, and they cannot be stored for extended periods. We have developed air-stable, storable, and highly efficient chiral zirconium Lewis acids. The catalysts promoted asymmetric Mannich-type, aza Diels-Alder, aldol, and hetero Diels-Alder reactions efficiently with high enantioselectivities. A key to stabilizing the catalysts is an appropriate combination of chiral zirconium Lewis acids with molecular sieves, and the zirconium-molecular sieves-combined catalysts can be stored for extended periods in air at room temperature without loss of activity. Moreover, it has been demonstrated that the catalysts can be recovered and reused. 相似文献
993.
994.
Genomic imprinting of XX spermatogonia and XX oocytes recovered from XX<-->XY chimeric testes 下载免费PDF全文
Isotani A Nakanishi T Kobayashi S Lee J Chuma S Nakatsuji N Ishino F Okabe M 《Proceedings of the National Academy of Sciences of the United States of America》2005,102(11):4039-4044
We produced XX<-->XY chimeras by using embryos whose X chromosomes were tagged with EGFP (X*), making the fluorescent green female (XX*) germ cells easily distinguishable from their nonfluorescent male (XY) counterparts. Taking advantage of tagging with EGFP, the XX* "prospermatogonia" were isolated from the testes, and the status of their genomic imprinting was examined. It was shown that these XX cells underwent a paternal imprinting, despite their chromosomal constitution. As previously indicated in sex-reversal XXsxr testes, we also found a few green XX* germ cells developed as "eggs" within the seminiferous tubules of XX*<-->XY chimeric testes. These cells were indistinguishable from XX* prospermatogonia at birth but resumed oogenesis in a testicular environment. The biological nature of the "testicular eggs" was examined by recovering the eggs from chimeric testes. The testicular eggs not only formed an egg-specific structure, the zona pellucida, but also were able to fuse with sperm. The collected testicular eggs were indicated to undergo maternal imprinting, despite the testicular environment. The genomic imprinting did not always follow the environmental conditions of where the germ cells resided; rather, it was defined by the sex that was chosen by the germ cells at early embryonic stage. 相似文献
995.
The worldwide reemergence of tuberculosis is significant. In particular, the incidence of extrapulmonary tuberculosis is increasing. But tuberculous tenosynovitis is rare and may be overlooked as a cause of chronic tenosynovitis. Here, we present a case of a 24 year-old man with a mass lesion on the flexor side of the right wrist. Laboratory findings were generally negative, except for the acceleration of the erythrocyte sedimentation rate, and the tuberculosis skin test was strongly positive. Magnetic resonance imaging (MRI) of the mass lesion of the wrist revealed tenosynovitis. We performed open biopsy and mycobacterial cultures. Thus, we diagnosed the patient with tuberculous tenosynovitis. Tuberculous tenosynovitis is uncommon but should be kept in mind in cases of chronic tenosynovitis. 相似文献
996.
Establishment of medaka (Oryzias latipes) transgenic lines with the expression of green fluorescent protein fluorescence exclusively in germ cells: a useful model to monitor germ cells in a live vertebrate 下载免费PDF全文
Tanaka M Kinoshita M Kobayashi D Nagahama Y 《Proceedings of the National Academy of Sciences of the United States of America》2001,98(5):2544-2549
We have generated transgenic medaka (teleost, Oryzias latipes), which allow us to monitor germ cells by green fluorescent protein (GFP) fluorescence in live specimens. Two medaka strains, himedaka (orange-red variety) and inbred QurtE, were used. The transgenic lines were achieved by microinjection of a construct containing the putative promoter region and 3' region of the medaka vasa gene (olvas). The intensity of GFP fluorescence increases dramatically in primordial germ cells (PGCs) located in the ventrolateral region of the posterior intestine around stage 25 (the onset of blood circulation). Whole-mount in situ hybridization and monitoring of ectopically located cells by GFP fluorescence suggested that (i) the increase in zygotic olvas expression occurs after PGC specification and (ii) PGCs can maintain their cell characteristics ectopically after stages 20-25. Around the day of hatching, the QurtE strain clearly exhibits sexual dimorphisms in the number of GFP fluorescent germ cells, a finding consistent with the appearance of leucophores, a sex-specific marker of QurtE. The GFP expression persists throughout the later stages in the mature ovary and testis. Thus, these transgenic medaka represent a live vertebrate model to investigate how germ cells migrate to form sexually dimorphic gonads, as well as a potential assay system for environmental substances that may affect gonad development. The use of a transgenic construct as a selective marker to efficiently isolate germ-line-transmitting founders during embryogenesis is also discussed. 相似文献
997.
Flower‐like/clover leaf lymphocytes appear in various diseases: Cerebrospinal fluid cytology case with review of the literature 下载免费PDF全文
998.
Value of thyroid specific peroxidase and Ki‐67 stains in preoperative cytology for thyroid follicular tumors 下载免费PDF全文
999.