N-Methoxy-N-acylnitrenium ions (11), generated by treatment of N-chloro-N-methoxyamides with silver carbonate in trifluoroacetic acid, react with arenes to give N-aryl-N-methoxyamides in good yields. In the case of the intramolecular cyclization of N-chloro-N-methoxy-2-phenylacetamides, the mode of cyclization is highly dependent on the nature of ortho or para substituent groups. Nitrenium ions I1 can primarily attack three positions (C-1, C-2, and C-6) of a phenyl ring. Normally I1 attack C-6. On the other hand, when the ortho position was occupied with a substituent group, I1 attacked both C-2 and C-6, in the former case followed by a 1,2-substituent migration, which was proved by a deuterium labeling experiment. Especially, when a methoxy group is substituted on ortho or para position, I1 attack C-1 due to the effect of the electron-releasing methoxy group to give spiro dienone compounds 39. A general discussion of the utility and mechanistic details of these reactions is presented.
Fractionated extracts of persimmon (Diospyros kaki) peels were studied for cytotoxic activity, multidrug resistance (MDR) reversal activity, anti-human immunodeficiency virus (HIV) activity and anti-Helicobacter pylori (H. pylori) activity. The potent cytotoxic activity against human oral squamous cell carcinoma cells (HSC-2) and human submandibular gland tumor (HSG) cells was found in the acetone fractions (A4 and A5) with IC(50) ranging from 21 to 59 micro g/mL. However, the cytotoxic activity was not correlated with the radical intensity of the fractions. Three 70% MeOH extract fractions (70M2-4) produced radical and efficiently scavenged the O(2)(-) produced by hypoxanthine and xanthine oxidase reaction. All of the fractions tested were not effective for anti-H. pylori and anti-HIV. Fractions H3 and H4 of hexane extract, and M2 and M3 of MeOH extract showed a remarkable MDR reversal activity comparable with that of (+/-)-verapamil (a positive control). These results indicate the therapeutic value of persimmon peel extracts as potential antitumor and MDR-reversing agents.
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