Allantoin is a product of adenine and guanine metabolism. Allantoin exists as two enantiomers (R)-(-)-allantoin and (S)-(+)-allantoin that are subject to enzimatic racemization. The spontaneous decomposition of upstream intermediates and the nonenzymatic racemization of allantoin lead to an accumulation of (R)-allantoin, because the enzymes converting allantoin into allantoate are specific for the (S) isomer. The enzyme allantoin racemase catalyzes the reversible conversion between the two allantoin enantiomers, thus ensuring the overall efficiency of the catabolic pathway and preventing allantoin accumulation. The naturally-occurring (+)-allantoin was isolated from leaves of Platanus orientah and from the urine of cattle. (-)-Allantoin was obtained by degradation of the dextrorotatory form of the racemate by allantoinase from soy bean meal or from the liver of Raja clavata.

D-(-)-tartaric acid is isomer of tartaric acid, that industrially produced in the largest amounts. D-(-)-Tartaric acid may be used in the preparation of enantiospecific homochiral cis-4-formyl β-lactams. It may also be used as a starting material in the synthesis of D-erythro-sphingosine and L-lyxo-phytosphingosine. D-(-)-tartaric acid is widely used as an acidizing agent for beverages and other foods, and this use is similar to citric acid. Tartaric acid can be used as an acid dye mordant when it is combined with tannin. It is also used for some development and fixing operations in the photographic industry. D-(-)-Tartaric Acid is used in the preparation of synthetic analgesics. Tartaric acid is metabolically inert in the human body. When taken by mouth, only about 20% of ingested tartrate is eliminated in the urine; the remainder is not absorbed as such since it is destroyed in the intestinal tract by bacterial action. Sodium tartrate in daily doses of up to 10 or even 20 g has been used in medical practice as a laxative.