PHASE II: Conjugation Reaction R O S E L Y N A. N A R A N J O

CONJUGATION REACTION Glucuronic acid conjugation Sulfate conjugation Conjugation with Glysine, Glutamine, and other AA Glutathione or Mercapturic Acid Conjugation Acetylation Methylation

Does not always produce hydrophilic or inactive metabolites Form more polar and water soluble products Enzymes attach small, polar and ionizable molecules (glucuronic acid, sulfate, glycine and glutamine) to the Phase I metabolites or to parent xenobiotics. Conjugating group includes glucuronic acid, sulfate, methyl and acetyl groups Regarded as a truly detoxifying pathway in drug metabolism CONJUGATION REACTION

GLUCURONIC ACID CONJUGATION Glucuronidation is the most common conjugative pathway in drug metabolism for the following reasons:  Readily available supply of d-glucuronic acid (from glucose)  Numerous functional groups that combine enzymatically with glucuronic acid  Glucuronyl moiety, polar hydoxyl groups which greatly increases water solubility when attached to the xenobiotics substrate. Combine with chemically reactive compound to form to prevent damage to important biomolecules

Formation of ß-glucuronides involves two steps:  synthesis of an coactivated enzyme (uridine- 5’diphopho, ∂-D glucoronic acid (UDPGA)  Transfer of the glucuronyl group from UDPGA to an appropriate substrate. GLUCURONIC ACID

A. OXYGEN GLUCURONIDES a.1 Hydroxyl Compounds -Phenols: morphine, acetaminophen, p- hydroxyphenytoin -Alcohols: trichloroethanol, chloramphenicol, propranolol -Enols: 4-hydroxycoumarin -N-Hydroxyamides: N-hydroxydapsone, N- hydroxy-2-acetylaminoflourene FUNCTIONAL GROUPS THAT UNDERGO GLUCURONIDATION

a.2 Carbonyl Compounds -Aryl acids: benzoic acids, salicylic acid -Arylalkyl acids: Naproxen, Fenoprofen B. NITROGEN GLUCURONIDES - Arylamines: 7-amino-5-nitroindazole -Arylamines: desipramine -Amides: meprobamate -Sulfonamides: Sulfisoxazole -Tertiary Amines: Cyproheptadine, tripelennamine FUNCTIONAL GROUPS THAT UNDERGO GLUCURONIDATION

C. SULFUR GLUCURONIDES -Sulfhydryl groups: methimazole, propylthiouracil, diethylthiocarbamic acid D. CARBON GLUCURONIDES -3,5Pyrazolidinedione: phenylbutazone, sulfinpyrazone FUNCTIONAL GROUPS THAT UNDERGO GLUCURONIDATION

GLUCURONIDATION PROCESS SHOWING THE SITE OF GLUCURONIDES ATTACHMENT TO THE METABOLITE MORPHINE(INSERT STRUCTURE) ACETAMINOPHEN PROPRANOLOL CHLORAMPHENICOL

SULFATE CONJUGATION Process occurs primarily with phenols, alcohols, aromatic amines, and N-hydoxy compounds. The body uses portion of sulfate pool to conjugate emdogenous compounds such as steroids, heparin, chondroitin, catecholamine, and thyroxine. Involves the activation of inorganic sulfate to its co-enzyme.

Phenols are main groups of substrates that undergo conjugation. Drug containing phenolic moiety are often susceptible to sulfate formation. SULFATE CONJUGATION

Conjugation with glycine, glutamine, and other Amino Cids Conjugates carboxylic acids particularly aromatic and arylaklyl acids. Example: (insert photo)  Benzoin Acid  Salicylic acid

Conjugation with GSH or Mercapturic acid Important pathway for detoxifying chemically reactive electrophilic compounds. Called glutamyl-cysteinylglycine (found in most tissues) Process involves enzymatic cleavage of two amino acid – glutamic acid and glycine) Its conjugation is catalyzed by an enzyme known as glutathione S-transferase. Degradation of GSH is due to renal and hepatic microsomal enzymes

Example: insert structure of brompheniramine Haloperidol, Diphenhydramine Conjugation with GSH or Mercapturic acid

ACETYLATION Constitutes a metabolic route for drugs containing primary amino groups, which includes the following:  Aromatic amines (ArNH 2 )  Sulfonamides (H 2 NC 6 H 4 SO 2 NHR)  Hydrazines (NHNH 2 )  Hydrazides (-CONHNH 2 )  Aliphatic amines

Derivatives formed from these amino functionalities are inactive and non-toxic. Its primary function is the termination of pharmacological activity and detoxification Less water solubility Acetyl group used is acetyl-CoA ACETYLATION

METHYLATION Inactivation of physiologically active biogenic amines Does not convert metabolites to become more water soluble except when it creates a quaternary ammonium derivative. Most of the products end up pharmacologically inactive

METHYLATION Foreign compounds that undergo methylation includes:  Cathecols,phenols, amines and N- heterocyclic and thiol compounds.  Anihypertensive drugs (methyldopa)  Antiparkinsonism agent (levodopa)  Norephenephrine and Dopamine

FACTORS THAT AFFECTS DRUG METABOLISM