Some novel isoxazole photochemistry: A comparison with vinyl azide chemistry

γ-Hydroxyalkynyl Ketones as Useful Scaffolds for the Preparation of Combinatorial Libraries of Furans, Isoxazoles and Pyrazoles

Using 5-hydroxy-hex-3-yne-2-one (9) as a model substrate, the utility of the gamma-hydroxyl alkynyl ketone scaffold for the preparation of combinatorial libraries of furans, isoxazoles, and pyrazoles is described. The addition of hydrazoic acid to the acetylenic ketone 9 forms in a single step both 3-azido-2,5-dimethyl furan (10) and alpha,5-dimethyl-3-isoxazolemethanol (11). Reaction of a mixture of (E)- and (Z)-bromoenediones (5 and 6), accessible from 3-bromo-2,5-dimethyl furan (17), with 1,1-dimethylhydrazine afforded a nearly quantitative yield of 1,3-dimethyl-5-acetylpyrazole (18). When the (E)- and (Z)-vinyl bromides 5 and 6 were reacted with sodium azide, 3-acetyl-5-methylisoxazole (7) formed via the intermediate (Z)-3-azido-3-hexene-2,5-dione (4), was the only product.

Anti-Helicobacter pylori agents. 5. 2-(Substituted guanidino)-4-arylthiazoles and aryloxazole analogues

To extend the SAR study of guanidinothiazoles as a structurally novel class of anti-H. pylori agents, a series of 2-(substituted guanidino)-4-arylthiazoles and some 4-aryloxazole analogues were synthesized and evaluated for antimicrobial activity against H. pylori. Some of them were also subjected to H2 antagonist and gastric antisecretory assays. Several arylthiazoles were identified as potent anti-H. pylori agents, and of these, thienylthiazole derivative 44 exhibited the strongest activity (MIC = 0.0065 microg/mL) among the compounds obtained in our guanidinothiazole studies. Although 44 was void of H2 antagonist activity, pyridylthiazole derivative 39 had both potent anti-H. pylori and H2 antagonist activities. Thiazolylthiazole derivative 46 also showed potent anti-H. pylori activity, but the H2 antagonist activity was weak. On the other hand, no attractive activities were found in pyrimidyl, oxazolyl, isoxazolyl, imidazolyl, and oxadiazolylthiazole derivatives. The anti-H. pylori activity of the aryloxazole analogues was weaker than those of the corresponding arylthiazole derivatives, though they had potent H2 antagonist activity.