On the behavior of alpha,beta-unsaturated thioaldehydes and thioketones in the Diels-Alder reaction.

Alpha,beta-unsaturated thioaldehydes and thioketones, R1CH=CH-C(=S)R2, are prepared in situ by the reaction between the corresponding carbonyl compounds and bis(dimethylaluminum) sulfide. These compounds undergo [4 + 2] self-dimerization reactions in which one molecule serves as the heterodiene component and the other as the dienophile to afford different types of dimeric products depending on the R1 and R2: 1,2-dithiin and 1,3-dithiin (R1 = R2 = H), 1,2-dithiin (R1 = Ph, R2 = H, CH3), or dihydrothiopyran (R1 = R2 = Ph). These differences in selectivity are explained on the basis of the relative energies evaluated by molecular orbital (MO) calculations at the DFT (density functional theory) level. The calculations show that in the dimerization reaction of thioacrolein (I), the head-to-tail (S-C-S bonded) dimers are kinetically more stable by about 5 kcal/mol but slightly thermodynamically unstable by about 2 kcal/mol than the head-to-head (S-S bonded) dimers. The calculations on thiocinnamaldehyde (IV) indicate that the dimerization reactions of phenyl-substituted alpha,beta-unsaturated thioaldehydes and thioketones are almost equally controlled by thermodynamic and kinetic factors. These unsaturated thiocarbonyl compounds also function as heterodienes (C=C-C=S) in the cycloaddition reaction with norbornadiene and as dienophiles (C=S) in the reaction with cyclopentadiene.

A case-control study of large bowel cancer in Japan.

This investigation of diet and other environmental factors reports on 588 patients with colorectal cancer and 1,176 hospitalized controls in three prefectures of Japan. Weak (not statistically significant) positive effects were found for social class and urbanization. The significant association of colorectal cancer with consumption of beef, string beans, or starches previously described for Hawaiian Japanese were not reproduced here. An association with hakusal (cabbage) agreed with other reports on a negative association with cruciferous vegetables. An analysis of the subset of cases in the low rectum yielded results similar to those for the total series. The failure to uncover important food effects in Japan is attributed to the difficulty of detecting case-control differences in areas with homogeneous diet practices. Further epidemiologic research aided by leads from ongoing work with animals may provide ideas for more sharply defined questions, should stress new approaches for more accurate diet histories, and should continue to emphasize tumor localization.

Stomach cancer in Japan.

A study of 783 patients with stomach cancer and 1,566 hospital controls in Hiroshima and Miyagi prefectures of Japan showed that farmers, representing mostly the lowest socioeconomic class, had higher risk of developing stomach cancer. The usual inverse gradient in risk by social class was in the urban population of Miyagi, but not Hiroshima, prefecture. The study in Japan did not reproduce the association of stomach cancer with consumption of salted/dried fish and salt-pickled vegetables described for the Hawaiian Japanese. Salted/dried fish and pickled vegetables were more widely used by farmers than by nonfarmers in Japan or by Japanese migrants to Hawaii. The ability to detect associations for these typical Japanese foods in Hawaii stemmed from the fact that these reduced levels of use were more completely expressed by the Hawaiian-Japanese controls than by patients. The lower risk of developing stomach cancer for lettuce and celery users agreed with the Hawaiian-Japanese findings, and the combined results supported conjectures on possible protective food effects. Lettuce, in particular, warranted attention from this viewpoint, since similar findings have been consistently reported.

Tea-gruel as a possible factor for cancer for the esophagus.

Specific death rates for esophageal cancer by each city and county in Japan were calculated. Nara and Wakayama Prefectures formed a high death-rate area with some neighboring cities and counties in other perfectures. Inhabitants of these area are known by the custom of taking "Chagayu", tea-cooked rice gruel. According to this survey on the habit of taking hot tea-gruel, with over 5,000 teachers and their families aged over 50 years old, the distribution of the precentages of taking tea-gruel among surveyed subjects by cities and counties was similar to that of the death rates for esophageal cancer. Also, in Yamaguchi Prefecture, western-most prefecture of the main island (Honshu), there was an area which showed a similar condition. The result of this survey suggests that taking hot tea-gruel is one of possible factors for esophageal cancer in these districts.