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Biomedical subjects

H C Shen

Publications and source records attributed to H C Shen.

7 recordsLinked to original sources
PubMed2001

Stereoselective trans- and cis-dihydroxylations of 2H-pyranyl and dihydropyridinyl heterocycles synthesized from formal [3 + 3]-cycloaddition reactions of alpha,beta-unsaturated iminium ions with 1,3-dicarbonyl equivalents.

[reaction: see text]We describe here an inherent problem in direct epoxidation of the endocyclic olefin in 2H-pyrans fused to 2-pyrones. Such difficulties led to the development of highly stereoselective trans- and cis-dihydroxylations of these olefinic systems in both 2H-pyrans and dihydropyridines fused to a 2-pyrones or a 2-cyclohexenone. Protocols for the removal of the activated allylic hydroxyl group are also reported.

Alkaloids↗
PubMed2000

On the regioselectivity of the Ru-catalyzed intramolecular [5 + 2] cycloaddition.

The influence of substituents on which cyclopropyl bond cleaves in the cycloisomerization of cyclopropylenynes catalyzed by CpRu(N&tbd1;CCH(3))(3)(+)PF(6)(-) is compared to the corresponding Rh-catalyzed reaction. With the trans cyclopropyl substrates, the bond energy of the cleaving bond appears to be an important factor. With cis cyclopropyl substrates, steric effects appear to dominate.

Alkenes↗
PubMed1999

Synthesis of dihydroxanthone derivatives and evaluation of their inhibitory activity against acetylcholinesterase: unique structural analogs of tacrine based on the BCD-ring of arisugacin.

A general approach to synthesis of dihydroxanthone derivatives is described here. In vitro evaluation of these dihydroxanthones demonstrated that some derivatives possess moderate anti-cholinesterase activities and better selectivities than tacrine for acetylcholinesterase over butyrylcholinesterase. Structural effects on anti-cholinesterase activities were also examined, and docking experiments were carried out to provide preliminary understandings of these experimental observations.

Acetylcholinesterase↗
PubMed1999

Recovery of Salmonella by using selenite brilliant green sulfa enrichment broth.

The efficacy and sensitivity of selenite brilliant green sulfa enrichment (SBG) broth for the isolation of Salmonella from fecal specimens were evaluated by using both clinical and artificially infected (artificial) fecal specimens. An examination of 1,588 clinical fecal specimens found Salmonella in 296 specimens, including 89 cases detected by the direct-plating xylose-lysine-desoxycholate method and an additional 207 cases detected after enrichment with SBG broth. Therefore, the recovery of Salmonella with SBG broth is increased 3.3-fold over that by the direct-plating method alone. Furthermore, the isolation rate of Salmonella is higher when using SBG broth than when using gram-negative (GN) broth or GN broth supplemented with sodium selenite. To determine the sensitivity for the recovery of Salmonella, artificial specimens containing various amounts of Salmonella were prepared and analyzed. The results indicated that the sensitivity is also higher with SBG broth than with GN broth. Moreover, the optimal incubation period for SBG broth can be extended to 24 h. In conclusion, the SBG enrichment method provides a higher recovery rate of Salmonella from fecal specimens.

Bacteriological Techniques↗
PubMed1991

Alzheimer's and Parkinson's disease. Brain levels of glutathione, glutathione disulfide, and vitamin E.

Human brain levels of glutathione (GSH), glutathione disulfide (GSSG), and vitamin E were measured in neurologically normal control patients and two groups of patients with neurodegeneration: those with Alzheimer's disease (AD), and AD with some features of Parkinson's disease (AD-PD). Control brain samples contained GSH levels more than 50 times higher than GSSG. The levels of GSH were highest in the caudate nucleus and lowest in the medulla. In patients with AD or AD-PD, hippocampal levels of GSH were significantly higher than controls. Patients with AD also demonstrated high GSH levels in the midbrain compared to normal. In contrast, patients with AD-PD did not have significantly elevated GSH levels in this site. GSSG levels were not significantly different in any brain region between controls and diseased patients. In control brains, the medulla had higher levels of vitamin E than any other brain region. The caudate nucleus had the lowest levels, which were about half the levels in the medulla. Control levels of vitamin E in the midbrain were about 18.8 micrograms/g. In AD patients the midbrain levels of vitamin E doubled to 42.3 micrograms/g. This doubling also occurred in AD-PD patients where midbrain vitamin E levels increased to 44.0 micrograms/g. These results may indicate that compensatory increases in GSH and vitamin E levels occur following damage to specific brain regions in patients with AD or AD-PD.

Aged↗
PubMed1988

[Rectal examination for extent of perirectal infiltration in rectal carcinoma].

From 1983 to 1985, 214 patients with rectal carcinoma were assessed for the conformation rate of the rectal examination to the gross findings of the extent of perirectal infiltration in the resected specimens. It was found that the conventional classification of the extent of rectal infiltration by rectal examination, 1/4, 1/3, 2/4, 3/4 and 4/4 of the circumference, had only a conformation rate of 32.7% to the gross findings. According to the classification of 1/4 or less and more, the conformation rate could reach 93%. It was also found that the extent of perirectal infiltration, being closely related to the regional lymph node metastasis and the depth of invasion, was only demonstrated by this latter classification, which was not shown in the conventional classification. Hence, it is suggested that the rectal examination implying the extent of perirectal infiltration by simply classified into two groups: equal to or less than 1/4 and more than 1/4 of the circumference of the rectal wall.

Humans↗