Vitamin C is present almost universally in the plant and animal kingdoms. (According to Linus Pauling, mountain goats biosynthesize from 12 to 14 g of it per day.) Animals produce it from D-glucose in the liver by the four-step sequence D-glucose → D-glucuronic acid (see Problem 62) →  D-glucuronic acid γ-lactone n l-gulonic acid γ-lactone → vitamin C. 

The enzyme that catalyzes the last reaction, L-gulonolactone oxidase, is absent from humans, some monkeys, guinea pigs, and birds, presumably because of a defective gene resulting from a mutation that may have occurred some 60 million years ago. As a result, we have to get our vitamin C from food or make it in the laboratory. In fact, the ascorbic acid in almost all vitamin supplements is synthetic. An outline of one of the major commercial syntheses follows. Draw the missing reagents and products (a) through (f ). 

Problem 62

Transcribed Image Text:

CH,OH OH Н-С—ОН HO. -C-H is the same as С-ОН H-C-0 С-ОН НО-С—Н C=0 CH,OH Vitamin C