Acetaminophen, also known as paracetamol, is commonly used for its analgesic and antipyretic effects. Its therapeutic effects are similar to salicylates, but it lacks anti-inflammatory, antiplatelet, and gastric ulcerative effects. Acetaminophen (USAN) or Paracetamol (INN) is a widely used analgesic and antipyretic drug that is used for the relief of fever, headaches, and other minor aches and pains. It is a major ingredient in numerous cold and flu medications and many prescription analgesics. It is extremely safe in standard doses, but because of its wide availability, deliberate or accidental overdoses are not uncommon. Acetaminophen, unlike other common analgesics such as aspirin and ibuprofen, has no anti-inflammatory properties or effects on platelet function, and it is not a member of the class of drugs known as non-steroidal anti-inflammatory drugs or NSAIDs. At therapeutic doses, acetaminophen does not irritate the lining of the stomach nor affect blood coagulation, kidney function, or the fetal ductus arteriosus (as NSAIDs can). Acetaminophen is thought to act primarily in the CNS, increasing the pain threshold by inhibiting both isoforms of cyclooxygenase, COX-1, COX-2, and COX-3 enzymes involved in prostaglandin (PG) synthesis. Unlike NSAIDs, acetaminophen does not inhibit cyclooxygenase in peripheral tissues and, thus, has no peripheral anti-inflammatory affects. Acetaminophen indirectly blocks COX, and that this blockade is ineffective in the presence of peroxides. This might explain why acetaminophen is effective in the central nervous system and in endothelial cells but not in platelets and immune cells, which have high levels of peroxides. Studies also report data suggesting that acetaminophen selectively blocks a variant of the COX enzyme that is different from the known variants COX-1 and COX-2. This enzyme is now referred to as COX-3. Its exact mechanism of action is still poorly understood, but future research may provide further insight into how it works. The antipyretic properties of acetaminophen are likely due to direct effects on the heat-regulating centers of the hypothalamus resulting in peripheral vasodilation, sweating and hence heat dissipation.

(R)-Ibuprofen, a nonsteroidal anti-inflammatory, is the less active enantiomer of ibuprofen. (S)-enantiomer of ibuprofen has the desired therapeutic effect (160 times more active than its (R)-enantiomer) in the in vitro inhibition of prostaglandin synthesis, while the (R)- ibuprofen is inactive. The accumulation of (R)- ibuprofen can cause serious side effects to the human body such as gastrointestinal pain and production of “hybrid” triglycerides between (R)- ibuprofen and Coenzyme A, which disrupt normal lipid metabolism and membrane function. The R(-)-isomer is almost inactive in inhibiting COX-2.

The methyl ester of ibuprofen is the most common starting material for the enzymatic resolution process based on selective hydrolyses of racemic mictures of ibuprofen esters. Addition of the methyl ester of racemic ibuprofen to growing cultures of Pseudomonas, Mucor, Arthrobacter or Bacillus species produced (S)-(+)-ibuprofen in 74-98% ee. Lipase from Candida rugosa hydrolyses racemic ibuprofen methyl ester to give 95% ee (S)-(+)-ibuprofen.