Structure – Activity Relationship of Sulphonamides – PST05106 Pharmaceutical Organic Chemistry
NTA Level 5 • Semester 1 • PST05106 Structure – Activity Relationship of Sulphonamides Pharmaceutical Organic Chemistry • Source Session/Topic 29 Full source-text version: all educational wording from the extracted learning source is retained; only presenter/tutor metadata and web-layout noise are removed, while formatting is improved for readability. Session 29: Structure – Activity Relationship of Sulphonamides. Total Session Time: 120 minutes Prerequisites None Learning Tasks By the end of this session students are expected to be able to: • Define Sulphonamides • Explain chemical structure of sulphonamides • Explain the structure – activity relationship of sulphonamides Resources Needed: • Flip charts, marker pens, and masking tape • Black/white board and chalk/whiteboard markers SESSION OVERVIEW |Step |Time |Activity/ |Content | | | |Method | | |1 |05 minutes |Presentation |Introduction, Learning Tasks | |2 |10 minutes |Brainstorming |Definition of Sulphonamides. | | | |Presentation | | |3 |40 minutes |Presentation |Chemical Structure of Sulphonamides.| |4 |45 minutes | Group |Structure – Activity Relationship of| | | |discussion |Sulphonamides. | | | |Presentation | | |5 |10 minutes |Presentation |Key Points | | 6 |10 minutes |Presentation |Evaluation | SESSION CONTENTS. STEP 1: Presentation of Session Title and Learning Tasks (5 minutes) READ or ASK students to read the learning tasks and clarify. ASK students if they have any questions before continuing. STEP 2: Definition of Sulphonamides (10 minutes). |Activity: Brainstorming (5 minutes) | | | |Ask students to brainstorm on the following question: | | | |What are Sulphonamides? | | | |ALLOW few students to respond. | | | |WRITE their responses on the flip chart/ board. | | | |CLARIFY and SUMMARISE by using the table below | Sulphonamides are antibacterial agents which acts against cell metabolism (antimetabolites). Sulfonamides: • Once known as ‘wonder drug’. • Once mainstays of antimicrobial chemotherapy. • The relative cheapness of the sulphonamides is one of their most attractive features and accounts for much of their persistence in the market. STEP 3: Chemical Structure of Sulphonamides (40 minutes). • Sulphonamides are composed of a sulphur atom that has two sets of double bonds to two oxygen atoms, a carbon-based side group, and a nitrogen atom bonded to the sulphur itself. • In organic chemistry, an amide contains a carbonyl group bonded to a nitrogen atom. • Sulphonamides are similar, but the carbonyl group is replaced with sulfone sulphur with two oxygen atoms). • That's why the term 'amide' appears in the name. [pic] General structure of amides and sulphonamides. • The 'R' groups in the figure simply represent any generic carbon-based side chain and could be virtually anything. • For example, R could be a methyl group, a benzene ring, an alkane ring, or some other group. • If the nitrogen atom contains two hydrogens, the sulphonamide is classified primary, if there is one hydrogen it's secondary, and if no hydrogens are present on the nitrogen, it's a tertiary sulphonamide [pic] Structures of primary, secondary, and tertiary sulphonamides. Important Sulfonamide Derivatives • Sulfamethoxazole • Sulfamethoxazole is another sulfonamide with antibacterial activity and is commonly used in the treatment of urinary tract infections and bronchitis. • Sulfamethoxazole looks very similar to sulfanilamide in terms of its structure but contains an extra ring system called an oxazole. [pic] STEP 4: Structure – Activity Relationship of Sulphonamides (45 minutes). |Activity: Small Group Discussion (20 minutes). | | | |DIVIDE students into small manageable groups. | | | |ASK students to discuss on the following question. | |What is the importance of SAR of sulphonamides? | | | |ALLOW students to discuss for 15 minutes. | | | |ALLOW few groups to present and the rest to add points not mentioned. | | | |CLARIFY and SUMMARIZE by using the contents below | The synthesis of a large number of sulphonamide analogues led to the following conclusions [pic] Sulfonamides analogues • The para -amino group is essential for activity and must be unsubstituted (i.e. R1=H). The only exception is when R1=acyl (i.e. amides). • The amides themselves are inactive but can be metabolized in the body to regenerate the active compound. • Thus, amides can be used as sulfonamide prodrugs. • Incorporation of other groups (halogen, alkyl, etc.) destroys the activity. [pic] Metabolism of acyl group to regenerate active compound • The aromatic ring and the sulphonamide functional group are both required. • Total loss of antibacterial activity occurs if sulphonamide group is replaced by other acidic groups (sulfonic, phosphoric etc.) • The aromatic ring must be para -substituted only. • Extra substitution eliminates activity for steric reasons. • The sulfonamide nitrogen must be primary (sulfanilamide) or secondary (acidic proton is essential for antibacterial activity). • R2 is the only possible site that can be varied in sulfonamides. Sulphonamide analogues • R2 can be varied by incorporating a large range of heterocyclic or aromatic structures, which affects the extent to which the drug binds to plasma protein. • This in turn controls the blood levels of the drug such that it can be short acting or long acting. • Thus, a drug which binds strongly to plasma protein will be slowly released into the blood circulation and will be longer lasting. • R2 affects pharmacokinetic properties but not the pharmacodynamics properties. Sulfonamide analogues with reduced toxicity • Changing the nature of the group R2 has also helped to reduce the toxicity of some sulfonamides. • The primary amino groups of sulfonamides are acetylated in the body and the resulting amides have reduced solubility which can lead to toxic effects. • For example, the metabolite formed from sulfathiazole is poorly soluble and can prove fatal if it blocks the kidney tubules [pic] Insoluble • It was discovered that the solubility problem could be overcome by replacing the thiazole ring in sulfathiazole with a pyrimidine ring to give sulfadiazine. [pic] • Its metabolites will also be water soluble • The reason for the improved solubility lies in the acidity of the sulphonamide NH proton. • In sulfathiazole, this proton