Medicinal Chemistry Key Definitions

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Active Transport	Carriage of solute across biological membrane from low to high concentration that requires the expenditure of metabolic energy.
Address-Message Concept	Compounds in which part of the molecule is required for binding (address) and part for the biological action (message)
ADME	Abbreviation of Absorption, Distribution, Metabolism and Excretion.
Affinity	Tendency of molecules to associate with each other, for drugs its ability to bind to target.
Agonist	Endogenous substance or drug that can interact with receptor and initiate a physiological or pharmacological response characteristic of that receptors.
Allosteric Binding Sites.	Contained in many enzymes and receptors, consequence of binding, the interaction with normal ligand may be either enhance or reduced.
Allosteric Enzyme	Enzyme that contain region to which small, regulatory molecules may bind in addition to and separate from substrate binding site, affecting catalytic activity.
Allosteric Regulation	Regulation of activity of allosteric enzyme
Analog	Drug whose structure is related to that of another drug, but whose properties may be different.
Antagonist	Drug/compound that opposes physiological effect of another, receptor level; it's a chemical entity that opposes receptor-associated responses normally induced by another bioactive agent/
Antimetabolite	Structure analog of an intermediate in a physiologically occurring metabolic pathway that acts by replacing the natural substrates thus blocking/diverting the biosynthesis of the physiologically importing substances.
Antisense Molecule	Oligonucleotide or analog that's complementary to RNA/DNA segment and that binds to it and inhibits its normal function.
Autacoid	Biological substance secreted by various cells whose physiological activity is restricted to the vicinity of its released, often referred as local hormone.
Autoreceptor	Present at a nerve ending, receptor that regulates, via positive or negative feedback processes, the synthesis and/or release of its own physiological ligand.
Bacteriocidal	Compound whose mechanism of action leads directly to cell death.
Bacteriostatic	Compound that stops bacterium growing or reproducing but does not kill it directly.
Bioassay	Procedure for determining concentration, purity and/or biological activity of substance by measuring its effect on organism, tissue, cell, enzyme or receptor preparation compared to standard.
Bioisotere	Compound resulting from exchange of an atom or group of atoms with another similar atom(s). Objective is to create new compound with similar biological properties, the replacement may be physiochemically or topologically based.
Bioprecursor Produrg	Prodrug that does not imply linkage to carrier group, results from molecular modification of active principle. Modification generates new compound, able to be transformed metabolically or chemically, resulting compound being active principle.
Biotransformation	Chemical conversion of substance by living organisms or enzyme preparations.
Carrier-Linked Prodrug	Prodrug that contains temporary linkage of given active substance with transient carrier groups, produces improved physicochemical/pharmacokinetic properties that can be easily removed in vivo, usually via hydrolytic cleavage.
Cascade Prodrug	Prodrug in which the cleavage of carrier group becomes effective only after unmasking of an activating group.
Catabolism	Reactions involving endogenous organic substrates to provide chemically available energy and/or to generate metabolic intermediates used in subsequent anabolic reactions.
Catabolite	Naturally occurring metabolite
Clone	Clone of population of genetically identical cells produced from common ancestor, also can be used for number of recombinant DNA molecules all carrying the same inserted sequence.
Codon	Sequence of three consecutive nucleotide that occurs in mRNA which directs incorporation of specific amino acid into protein or represents starting or termination signals of protein synthesis.
Coenzyme	Dissociable, low molecular weight, non-proteinaceous organic compound participating in enzymatic reactions as acceptors or donors of chemical groups or electrons.
Combinatorial Synthesis	Process to prepare large sets of organic compounds by combining sets of building blocks
Combinatorial Library	Set of compounds prepared by combinatorial synthesis
Comparative Molecular Field Analysis (CMFA)	3D-QSAR method that uses statistical correlation technique for analysis of quantitative relationship between biological activity of set of compounds with specified alignment, and their three-dimensional electronic and steric properties.
Computational Chemistry	Discipline using mathematical methods for calculations of molecular properties or for simulation of molecular behaviour.
Computer-Assisted Drug Design	Involves all computer-assisted techniques used to discover, design and optimise biologically active compounds with a putative use as drugs.
Congener	Substance synthesised by essentially the same synthetic chemical reactions and the same procedure, analogs are substances that are analogous in some respects to prototype agent in chemical structure.
Cooperativity	Interaction process by which binding of a ligand to one site on macromolecule influences binding at second site. Cooperative enzymes typically display a sigmoid plot of reaction rate against substrate concentration.
De Novo Design	Design of bioactive compounds by incremental construction of ligand model within a model of the receptor/enzyme active site, the structure which is known from X-Ray or NMR data.
Distomer	Enantiomer of chiral compound that's less potent for particular action.
Docking Studies	Molecular modelling studies aiming at finding proper fit between a ligand and its binding site.
Double-Blind Study	Clinical study of potential and marketed drugs, where neither the investigators nor the subjects know which subjects will be treated with the active principle and which one will receive a placebo.
Double Prodrug/Pro-prodrug	Biologically inactive molecule that is transformed in vivo in two steps to the active species.
Drug	Substance presented for treating, curing or preventing diseases, may also be used for making a medical diagnosis or for restoring, correcting or modifying physiological function.
Drug Disposition	Refer to all processes involved in absorption, distribution metabolism and excretion of drugs in a living organism.
Drug Latentiation	Chemical modification of biologically active compound to form new compound, which in vivo will liberate the parent compound.
Drug targeting	Strategy aiming at the delivery of compound to a particular tissue of the body.
Dual Action Drug	Compound which combines two desired different pharmacological actions at a similarly efficacious dose.
Efficacy	Describe relative intensity with which agonists vary in response they produce even when they occupy the same number of receptors and with the same affinity.
Elimination	Process achieving the reduction of the concentration of a xenobiotic including its metabolism.
Enzyme	Macromolecule that functions as a catalyst by increasing reaction rate.
Enzyme Induction	Process whereby an enzyme is synthesised in response to a specific inducer molecule.
Enzyme Repression	Mode by which synthesis of enzyme is prevented by repress molecules.
Eudismic Ratio	Potency of the eutomer relative to that of the distomer.
Eutomer	Enantiomer of chiral compound that's more potent for a particular action.
Genome	Complete set of chromosomal and extrachromosomal genes of an organism, cell, organelle or virus; the complete DNA component of an organism.
Hansch Analysis	Investigation of quantitative relationship between biological activity of series of compounds and their physiochemical substituent or global parameters representing hydrophobic, electronic, steric and other effects using multiple regression correlation methodology.
Hapten	Low molecular weight molecule that contains an antigenic determinant but which is not itself antigenic unless combined with an antigenic carrier.
Hard Drug	Non-metabolizable compound, characterised either by high lipid solubility and accumulation in adipose tissue and organelles, or by high water solubility.
Heteroreceptor	Receptor regulating the synthesis and/or release of mediators other than its own ligand.
Homologue	Used to describe a compound belonging to a series of compounds differing from each other by a repeating unit.
Hormone	Substance produced by endocrine glands, released in very low concentration into the bloodstream, and which exerts regulatory effects on specific organs or tissues distant from the site of secretion.
Hydrophilicity	The tendency of a molecule to be solvated by water.
Hydrophobicity	Association of non-polar groups or molecules in an aqueous environment which arises from the tendency of water to exclude non-polar molecule.
Intrinsic Activity	Maximal stimulatory response induced by a compound in relation to that of a given reference compound.
Inverse Agonist	Drug that acts at the same receptor as that of an agonist, yet produces an opposite effect.
Isoteres	Molecules or ions of similar size containing the same number of atoms and valence electrons.
Lead Discovery	Process of identifying active new chemical entities, which by subsequent modification may be transformed into a clinically useful drug.
Lead Generation	Term applied to strategies developed to identify compounds which posses a desired but non-optimized biological activity.
Lead Optimization	Synthesis and modification of a biologically active compound to fulfill all stereoelectronic, physiochemical, pharmacokinetic and toxicologic required for clinical usefulness.
Lipophilicty	Affinity of a molecule or a moiety for a lipophilic environment.
Mechanism-based inhibitor	Compound that is processed by an enzyme as a normal substrate until a highly reactive intermediate is generated that forms a permanent covalent bond to the enzyme/coenzyme, irreversibly inhibiting the enzyme.
Medicinal Chemistry	Chemistry-based discipline, also involving aspects of biological, medical and pharmaceutical sciences.
Metabolism	Entire physical and chemical processes involved in the maintenance and reproduction of life in which nutrients are broken down to generate energy and to give simpler molecule which by themselves may be used to form more complex molecules.
Metabolite	Any intermediate or product resulting from metabolism
Me-too Drug	Compound that is structurally very similar to already known drug, with only minor pharmacological differences.
Molecular Graphics	Visualisation and manipulation of three-dimensional representations of molecules on a graphical display device.
Molecular Modelling	Technique for investigating molecular structures and properties using computational chemistry and graphical visualisation techniques in order to provide a plausible 3D representation under a given set of circumstances.
Mutagen	Agent that causes a permanent heritable change into the DNA of an organism.
Mutual Prodrug	Association in a unique molecule of two, usually synergistic, drugs attached to each other, one drug being the carrier for the other and vice versa.
New Chemical Entity (NCE)	Compound not previously described in literature
Nucleic Acid	Macromolecule composed of linear sequences of nucleotides that perform several functions in living cell.
Nucleoside	Compound in which a purine or pyrimidine base is bound via a N-atom to C-1 replacing the hydroxyl group of either 2-deoxy-D-ribose or D-ribose, but without any phosphate groups.
Nucleotide	Nucleoside in which the primary hydroxyl group is esterified by orthophosphoric acid.
Oligonucleotide	Oligomer resulting from a linear sequence of nucleotides.
Oncogene	Normal cellular gene which, when inappropriately expressed/mutated, can transform eukaryotic cells into tumour cells.
Orphan Drug	Drug for treatment of rare disease for which reasonable recovery of the sponsoring firm's research and development expenditure is not expected within a reasonable time.
Partial Agonist	Agonist which is unstable to induce maximal activation of a receptor population, regardless of the amount of drug applied.
Pattern recognition	Identification of patterns in large data sets using appropriate mathematical methodologies.
Peptidomimetic	Compound containing non-peptide structural elements that is capable of mimicking or antagonising the biological actions of a natural parent peptide.
Peptoid	Peptidomimetic that results from the oligomeric assembly of N-Substituted glycines.
Pfeiffer's Rule	In a series of chiral compounds the eudismic ratio increases with increasing potency of the eutomer.
Phramacokinetics	Study of absorption, distribution, metabolism and excretion of bioactive compounds in higher organisms.
Pharmacophore	Ensemble of steric and electronic features that's necessary to ensure optimal supramolecular interactions with specific biological target structures and to trigger or to block its biological response.
Pharmacophoric Descriptors	Used to define pharmacophore including H-bonding, hydrophobic and electrostatic interaction sites, defined by atoms, ring centers and virtual points.
Placebo	Inert substance or dosage form which is identical in appearance, flavour and odour to the active substance or dosage form.
Potency	Dose of drug required to produce a specific effect of a given intensity as compared to a standard reference.
Prodrug	Any compound that undergoes biotransformation before exhibiting its pharmacological effects.
Quantitative Structure-Activity Relationships (QSAR)	Mathematical relationships linking chemical structure and pharmacological activity in quantitative manner for series of compounds.
Receptor	Molecule/polymeric structure in or on a cell that specifically recognises and binds a compound acting as molecular messenger.
Receptor Mapping	Technique used to describe the geometric and/or electronic features of a binding site when insufficient structural data for this receptor or enzyme are available.
Second Messenger	Intracellular metabolite or ion increasing/decreasing as a response to the stimulation of receptors by agonists, considered as the 'first messenger'.
Site-Specific Delivery	Approach to target a drug to specific tissue, using prodrugs or antibody recognition systems.
Site-specific Delivery	Approach to target a drug to a specific tissue, using prodrugs or antibody recognition system.
Soft Drug	Compound that is degraded in vivo to predictable non-toxic and inactive metabolite after having achieved its therapeutic role.
Strucutre-Activity Relationship (SAR)	Relationship between chemical structure and pharmacological activity for a series of compounds.
Structure-Based Drugs	Drug design strategy based on the 3D structure of the target obtained by x-ray or NMR
Structure-Property Correlations (SPC)	All statistical mathematical methods used to correlate any structural property to any other property using statistical regression and pattern recognition techniques.
Systematic	Relating to or affecting the whole body.
Teratogen	Substance that produces a malformation in a foetus.
3D-QSAR	Analysis of the quantitative relationship between the biological activity of a set of compounds and their spatial properties using statistical methods.
Topliss Tree	Operational scheme for analog design.
Transition-State Analog	Compound that mimics the transition state of a substrate bound to an enzyme
Xenobiotic	A compound foreign to an organism.
IC50	The concentration of inhibitor required to reduce the reaction velocity to half its value in the absence of the inhibitor.
Ki	The dissociation constant for all enzyme-inhibitor complexes: Image: Ki (binary/octet-stream)
ED50	Effective dose of a drug necessary to produce a therapeutic effect in 50% of the test sample.
LD50	Lethal dose of a drug required to kill 50% of the test sample.
Therapeutic Index	An indication of the safety of a drug based on a ratio of the drug dose level that produces toxic effects in 50% of the sample with respect to the dose level required for maximum therapeutic effect in 50% of the test sample. Higher the therapeutic ratio, the higher the tolerance to the drug.
Orphan Drug	A drug that would not be commercially viable to develop due to small market (<200,000 cases per year in USA) or occurrence of the disease only in third world countries.

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