Molecular modification

Last updated

Molecular modification is chemical alteration of a known and previously characterized lead compound for the purpose of enhancing its usefulness as a drug. This could mean enhancing its specificity for a particular body target site, increasing its potency, improving its rate and extent of absorption, modifying to advantage its time course in the body, reducing its toxicity, changing its physical or chemical properties (like solubility) to provide desired features.

Contents

Modification for water solubility

Molecular modification is used to enhance drug's water solubility by incorporating water solubilizing groups in its structure. The discussion of the introduction of water solubilizing groups into the structure of a lead compound can be conveniently broken down into four general areas:

The type of group

The incorporation of polar functional groups, such as the alcohol, amine, amide, carboxylic acid, sulfonic acid and phosphate groups, which either ionize or are capable of relatively strong intermolecular forces of attraction with water (hydrogen bonding), will usually result in analogues with an increased water solubility. Acidic and basic groups are particularly useful, since these groups can be used to form salts, which would give a wider range of dosage forms for the final product. However, the formation of zwitterions by the introduction of either an acid group into a structure containing a base or a base group into a structure containing an acid group can reduce water solubility. Introduction of weakly polar groups, such as carboxylic acid esters, aryl halides and alkyl halides, will not significantly improve water solubility and can result in enhanced lipid solubility.

The incorporation of acidic residues into a lead structure is less likely to change the type of activity, but it can result in the analogue exhibiting haemolytic properties. Furthermore, the introduction of an aromatic acid group usually results in anti-inflammatory activity, whilst carboxylic acids with an alpha functional group may act as chelating agents. Basic water solubilizing groups have a tendency to change the mode of action, since bases often interfere with neurotransmitters and biological processes involving amines. However, their incorporation does mean that the analogue can be formulated as a wide variety of acid salts. Non-ionizable groups do not have the disadvantages of acidic and basic groups.

Reversibly and irreversibly attached groups

The type of group selected also depends on the degree of permanency required. Groups that are bound directly to the carbon skeleton of the lead compound by less reactive C–C, C–O and C–N bonds are likely to be irreversibly attached to the lead structure.

Groups that are linked to the lead by ester, amide, phosphate, sulfate and glycosidic bonds are more likely to be metabolized from the resulting analogue to reform the parent lead compound as the analogue is transferred from its point of administration to its site of action. Compounds with this type of solubilizing group are acting as prodrugs and so their activity is more likely to be the same as the parent lead compound. However, the rate of loss of the solubilizing group will depend on the nature of the transfer route, and this could affect the activity of the drug.

The position of the water solubilizing group

In order to preserve the type of activity exhibited by the lead compound, the water solubilizing group should be attached to a part of the structure that is not involved in the drug–receptor interaction. Consequently, the route used to introduce a new water solubilizing group and its position in the lead structure will depend on the relative reactivities of the pharmacophore and the rest of the molecule. The reagents used to introduce the new water solubilizing group should be chosen on the basis that they do not react with, or in close proximity to, the pharmacophore. This will reduce the possibility of the new group affecting the relevant drug–receptor interactions.

Methods of introduction

Water solubilizing groups are best introduced at the beginning of a drug synthesis, although they may be introduced at any stage. Introduction at the beginning avoids the problem of a later introduction changing the type and/or nature of the drug–receptor interaction. A wide variety of routes may be used to introduce a water solubilizing group; the one selected will depend on the type of group being introduced and the chemical nature of the target structure. Many of these routes require the use of protecting agents to prevent unwanted reactions of either the water solubilizing group or the lead structure.

Acidic and basic groups

Examples of water solubilizing structures and the routes used to introduce them into the lead structures. O-alkylation, N-alkylation, O-acylation and N-acylation reactions are used to introduce both acidic and basic groups. Acetylation methods use both the appropriate acid chloride and anhydride.

Examples of water solubilizing structures and the routes used to introduce them into lead structures. Phosphate acid halides have been used to introduce phosphate groups into lead structures. Structures containing hydroxy groups have been introduced by reaction of the corresponding monochlorinated hydrin and the use of suitable epoxides amongst other methods. Sulphonic acid groups may be introduced by either direct sulfonation or the addition of bisulfite to reactive C = C bonds amongst other methods.

Related Research Articles

In organic chemistry, amines (, UK also ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group (these may respectively be called alkylamines and arylamines; amines in which both types of substituent are attached to one nitrogen atom may be called alkylarylamines). Important amines include amino acids, biogenic amines, trimethylamine, and aniline; see Category:Amines for a list of amines. Inorganic derivatives of ammonia are also called amines, such as monochloramine (NClH2).

Carboxylic acid Organic compound

A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic acids occur widely. Important examples include the amino acids and fatty acids. Deprotonation of a carboxylic acid gives a carboxylate anion.

Ester Chemical compounds consisting of a carbonyl adjacent to an ether linkage

An ester is a chemical compound derived from an acid in which at least one –OH hydroxyl group is replaced by an –O– alkyl (alkoxy) group, as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides are fatty acid esters of glycerol; they are important in biology, being one of the main classes of lipids and comprising the bulk of animal fats and vegetable oils.

Functional group Set of atoms in a molecule which augment its chemical and/or physical properties

In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest of the molecule's composition. This enables systematic prediction of chemical reactions and behavior of chemical compounds and the design of chemical synthesis. The reactivity of a functional group can be modified by other functional groups nearby. Functional group interconversion can be used in retrosynthetic analysis to plan organic synthesis.

In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively charged sodium ions and negatively charged chloride ions.

Acyl group

An acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen atom and an alkyl group (R-C=O). In organic chemistry, the acyl group is usually derived from a carboxylic acid. Therefore, it has the formula RCO–, where R represents an alkyl group that is linked to the carbon atom of the group by a single bond. Although the term is almost always applied to organic compounds, acyl groups can in principle be derived from other types of acids such as sulfonic acids, phosphonic acids. In the most common arrangement, acyl groups are attached to a larger molecular fragment, in which case the carbon and oxygen atoms are linked by a double bond.

Fischer–Speier esterification

Fischer esterification or Fischer–Speier esterification is a special type of esterification by refluxing a carboxylic acid and an alcohol in the presence of an acid catalyst. The reaction was first described by Emil Fischer and Arthur Speier in 1895. Most carboxylic acids are suitable for the reaction, but the alcohol should generally be primary or secondary. Tertiary alcohols are prone to elimination. Contrary to common misconception found in organic chemistry textbooks, phenols can also be esterified to give good to near quantitative yield of products. Commonly used catalysts for a Fischer esterification include sulfuric acid, p-toluenesulfonic acid, and Lewis acids such as scandium(III) triflate. For more valuable or sensitive substrates other, milder procedures such as Steglich esterification are used. The reaction is often carried out without a solvent or in a non-polar solvent to facilitate the Dean-Stark method. Typical reaction times vary from 1–10 hours at temperatures of 60-110 °C.

In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group -COCl. Their formula is usually written RCOCl, where R is a side chain. They are reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride, CH3COCl. Acyl chlorides are the most important subset of acyl halides.

In chemistry, acylation is the process of adding an acyl group to a compound. The compound providing the acyl group is called the acylating agent.

A nitrile is any organic compound that has a −C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, including methyl cyanoacrylate, used in super glue, and nitrile rubber, a nitrile-containing polymer used in latex-free laboratory and medical gloves. Nitrile rubber is also widely used as automotive and other seals since it is resistant to fuels and oils. Organic compounds containing multiple nitrile groups are known as cyanocarbons.

In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs. This kind of conversion is in fact so common that a comprehensive overview is challenging. This article mainly deals with halogenation using elemental halogens (F2, Cl2, Br2, I2). Halides are also commonly introduced using salts of the halides and halogen acids. Many specialized reagents exist for and introducing halogens into diverse substrates, e.g. thionyl chloride.

Acyl halide chemical compound

An acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group.

Organic acid anhydride Any chemical compound having two acyl groups bonded to the same oxygen atom

An organic acid anhydride is an acid anhydride that is an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the parent acid is a carboxylic acid, the formula of the anhydride being (RC(O))2O. Symmetrical acid anhydrides of this type are named by replacing the word acid in the name of the parent carboxylic acid by the word anhydride. Thus, (CH3CO)2O is called acetic anhydride. Mixed (or unsymmetrical) acid anhydrides, such as acetic formic anhydride (see below), are known, whereby reaction occurs between two different carboxylic acids. Nomenclature of unsymmetrical acid anhydrides list the names of both of the reacted carboxylic acids before the word "anhydride" (for example, the dehydration reaction between benzoic acid and propanoic acid would yield "benzoic propanoic anhydride").

Meldrums acid Chemical compound

Meldrum's acid or 2,2-dimethyl-1,3-dioxane-4,6-dione is an organic compound with formula C6H8O4. Its molecule has a heterocyclic core with four carbon and two oxygen atoms; the formula can also be written as [−O−(C 2)−O−(C=O)−(CH2)−(C=O)−].

Carbonyldiimidazole Chemical compound

1,1'-Carbonyldiimidazole (CDI) is an organic compound with the molecular formula (C3H3N2)2CO. It is a white crystalline solid. It is often used for the coupling of amino acids for peptide synthesis and as a reagent in organic synthesis.

Nucleophilic acyl substitution describe a class of substitution reactions involving nucleophiles and acyl compounds. In this type of reaction, a nucleophile – such as an alcohol, amine, or enolate – displaces the leaving group of an acyl derivative – such as an acid halide, anhydride, or ester. The resulting product is a carbonyl-containing compound in which the nucleophile has taken the place of the leaving group present in the original acyl derivative. Because acyl derivatives react with a wide variety of nucleophiles, and because the product can depend on the particular type of acyl derivative and nucleophile involved, nucleophilic acyl substitution reactions can be used to synthesize a variety of different products.

Organophosphorus compounds are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective insecticides, although some are extremely toxic to humans, including sarin and VX nerve agents.

Camptothecin

Camptothecin (CPT) is a topoisomerase inhibitor. It was discovered in 1966 by M. E. Wall and M. C. Wani in systematic screening of natural products for anticancer drugs. It was isolated from the bark and stem of Camptotheca acuminata, a tree native to China used in traditional Chinese medicine. It has been used clinically more recently in China for the treatment of gastrointestinal tumors. CPT showed anticancer activity in preliminary clinical trials, especially against breast, ovarian, colon, lung, and stomach cancers. However, it has low solubility and adverse effects have been reported when used therapeutically, so synthetic and medicinal chemists have developed numerous syntheses of camptothecin and various derivatives to increase the benefits of the chemical, with good results. Four CPT analogues have been approved and are used in cancer chemotherapy today, topotecan, irinotecan, belotecan, and trastuzumab deruxtecan. Camptothecin has also been found in other plants including Chonemorpha fragrans.

Phosphate solubilizing bacteria Bacteria

Phosphate solubilizing bacteria (PSB) are beneficial bacteria capable of solubilizing inorganic phosphorus from insoluble compounds. P-solubilization ability of rhizosphere microorganisms is considered to be one of the most important traits associated with plant phosphate nutrition. It is generally accepted that the mechanism of mineral phosphate solubilization by PSB strains is associated with the release of low molecular weight organic acids, through which their hydroxyl and carboxyl groups chelate the cations bound to phosphate, thereby converting it into soluble forms. PSB have been introduced to the Agricultural community as phosphate Biofertilizer. Phosphorus (P) is one of the major essential macronutrients for plants and is applied to soil in the form of phosphate fertilizers. However, a large portion of soluble inorganic phosphate which is applied to the soil as chemical fertilizer is immobilized rapidly and becomes unavailable to plants. Currently, the main purpose in managing soil phosphorus is to optimize crop production and minimize P loss from soils. PSB have attracted the attention of agriculturists as soil inoculums to improve the plant growth and yield. When PSB is used with rock phosphate, it can save about 50% of the crop requirement of phosphatic fertilizer. The use of PSB as inoculants increases P uptake by plants. Simple inoculation of seeds with PSB gives crop yield responses equivalent to 30 kg P2O5 /ha or 50 percent of the need for phosphatic fertilizers. Alternatively, PSB can be applied through fertigation or in hydroponic operations. Many different strains of these bacteria have been identified as PSB, including Pantoea agglomerans (P5), Microbacterium laevaniformans (P7) and Pseudomonas putida (P13) strains are highly efficient insoluble phosphate solubilizers. Recently, researchers at Colorado State University demonstrated that a consortium of four bacteria, synergistically solubilize phosphorus at a much faster rate than any single strain alone. Mahamuni and Patil (2012) isolated four strains of phosphate solubilizing bacteria from sugarcane (VIMP01 and VIMP02) and sugar beet rhizosphere (VIMP03 and VIMP 04). Isolates were strains of Burkholderia named as VIMP01, VIMP02, VIMP03 and VIMP04. VIMP (Vasantdada Sugar Institute Isolate by Mahamuni and Patil) cultures were identified as Burkholderia cenocepacia strain VIMP01 (JQ867371), Burkholderia gladioli strain VIMP02 (JQ811557), Burkholderia gladioli strain VIMP03 (JQ867372) and Burkholderia species strain VIMP04 (JQ867373)6].

Furegrelate

Furegrelate, also known as 5-(3-pyridinylmethyl)benzofurancarboxylic acid, is a chemical compound with thromboxane enzyme inhibiting properties that was originally developed by Pharmacia Corporation as a drug to treat arrhythmias, ischaemic heart disorders, and thrombosis but was discontinued. It is commercially available in the form furegrelate sodium salt.

References