thiamin

(thiamine, vitamin B₁) A substituted pyrimidine joined through a methylene bridge to a substituted thiazole. In its active form, thiamin pyrophosphate, it acts as a coenzyme in reactions involving the transfer of aldehyde  groups   in   carbohydrate  metabolism. Thiamin is synthesized by plants but not by some microorganisms or most vertebrates, which thus require it in the diet.