SAT (Silver-Amide-THC)

UDC: 547.551.525.211.1:546.57:615.212.7:542.91

SYNTHESIS AND PROSPECTS OF PHARMACOLOGICAL ACTIVITY OF HYBRID MOLECULES BASED ON SULFANILAMIDE MODIFIED WITH A SILVER ATOM AND TETRAHYDROCANNABINOL: THEORETICAL JUSTIFICATION AND SYNTHETIC APPROACHES

Author: Sukhachov Denуs Pavlovych

Abstract
Introduction. Modern medicinal chemistry is actively developing the direction of “polypharmacology,” creating hybrid molecules capable of simultaneously affecting several pathological targets. Sulfanilamides are classical antibacterial agents whose mechanism of action involves competitive antagonism with para-aminobenzoic acid (PABA). Meanwhile, cannabinoids, particularly Δ⁹-tetrahydrocannabinol (THC), demonstrate a wide range of pharmacological activities, including anti-inflammatory, analgesic, and immunomodulatory effects, realized through interaction with CB1 and CB2 receptors.
Objective. To theoretically substantiate the feasibility of synthesis, develop a detailed synthetic scheme, and predict the potential clinical effects of a novel hybrid molecule based on sulfanilamide, containing a silver atom in the ortho-position relative to the amino group and a THC residue in the meta-position.
Materials and Methods. An analysis of scientific literature on the structure and properties of sulfanilamides, the coordination chemistry of silver, the pharmacology of cannabinoids, and methods of organic synthesis, including protecting groups for amines, electrophilic aromatic substitution reactions, and cross-coupling reactions, was conducted. Based on the principles of structure-activity relationships (SAR), a hypothetical structure was modeled, and a retrosynthetic analysis of the target molecule was proposed.
Results. The general formula of the hybrid compound is proposed as: 2-Ag-5-THC-4-aminobenzenesulfonamide. A detailed 6-stage synthesis scheme was developed, including: (1) protection of the amino group by acylation; (2) selective iodination at position 5; (3) introduction of the THC residue via the Suzuki reaction using a THC boronic ester; (4) ortho-metalation to introduce the silver atom at position 2; (5) final deprotection under mild conditions. Key synthetic challenges are discussed: stability of the C-Ag bond, steric hindrance during the introduction of the bulky THC residue, and preservation of the free amino group. Three main directions of biological activity are theoretically predicted: antibacterial (due to the sulfanilamide fragment and the potential action of silver ions, analogous to silver sulfadiazine), anti-inflammatory and analgesic (due to the THC fragment). The issue of potential nephrotoxicity, characteristic of silver compounds, is considered.
Conclusions. The creation of hybrid molecules based on sulfanilamide, silver, and THC is a promising, albeit synthetically challenging, task. The proposed synthetic scheme can serve as a starting point for experimental implementation. The obtained compounds could form the basis for developing fundamentally new drugs with combined action for treating infected wounds, chronic pain syndromes, and inflammatory diseases.

Keywords: sulfanilamides, silver, tetrahydrocannabinol, hybrid molecules, medicinal chemistry, polypharmacology, organic synthesis, Suzuki reaction, protecting groups.

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1. INTRODUCTION

The “one molecule – one target” strategy has, in many cases, ceased to meet the challenges of modern pharmacotherapy, especially in the treatment of chronic, multifactorial diseases. This has led to the development of the concept of “polypharmacology,” where a single molecule is designed for the simultaneous modulation of several biological targets that have a synergistic therapeutic effect.

Sulfanilamides, due to their unique structure, are an attractive scaffold for such modification. Their mechanism of action is well-studied: they are structural analogs of para-aminobenzoic acid (PABA) and competitively inhibit the bacterial enzyme dihydropteroate synthase, blocking the synthesis of folic acid necessary for the growth of microorganisms. The synthesis of classical sulfanilamide involves acetylation of aniline to protect the amino group, subsequent chlorosulfonation, treatment with ammonia, and hydrolysis. The free para-amino group is an obligatory condition for antibacterial activity.

The introduction of metal atoms, particularly silver, into the structure of sulfanilamides is already known in clinical practice. The drug silver sulfadiazine (silver sulfadiazine, Sulfargin® ointment) is widely used for the topical treatment of infected wounds and burns, combining the bacteriostatic action of sulfanilamide with the bactericidal properties of silver ions. However, in this compound, silver forms a salt with the sulfanilamide nitrogen atom, rather than being located in the aromatic ring. It is important to note that silver compounds can exhibit nephrotoxicity upon systemic administration, which requires monitoring of renal function.

Phytocannabinoids, particularly THC, are ligands of the endocannabinoid system. Their therapeutic potential includes pain relief (especially in neuropathic pain), anti-inflammatory effects, reduction of nausea and vomiting, and appetite stimulation. Combining these effects with the antibacterial activity of sulfanilamides could create a unique drug for complex therapy.

The aim of this theoretical work is to substantiate the possibility of creating, develop a detailed synthetic scheme, and predict the properties of a hybrid molecule in which a silver atom is covalently introduced into the ortho-position, and a THC residue into the meta-position of the benzene ring of sulfanilamide relative to the free amino group.

2. MATERIALS AND METHODS

The study is theoretical in nature. The method of retrosynthetic analysis was used to assess the fundamental feasibility of synthesizing the target molecule. Prediction of biological activity was based on a comparative analysis of literature data on the pharmacology of sulfanilamides, silver compounds, and cannabinoids. Synthetic approaches were developed based on classical organic chemistry reactions: electrophilic aromatic substitution, methods for protecting amino groups, cross-coupling reactions, and metalation.

3. RESULTS AND DISCUSSION

3.1. Molecular Design and Nomenclature

Based on the aim of the study, the target molecule was designated as 2-Ag-5-THC-4-aminobenzenesulfonamide (Compound 6). Its structure includes three key fragments:

1. Sulfanilamide core: 4-aminobenzenesulfonamide with a free amino group (position 1 according to substituent nomenclature), necessary for antibacterial activity.
2. Silver atom (Ag): covalently bonded in the ortho-position (position 2) relative to the amino group.
3. THC residue: attached in the meta-position (position 5) relative to the amino group.

3.2. Retrosynthetic Analysis

Retrosynthetic analysis of target molecule 6 allows the identification of key synthetic transformations:

• Cleavage of the C-Ag bond: introduction of the silver atom at the final stage via ortho-metalation.
• Cleavage of the C-THC bond: formation of the bond between the aromatic ring and the THC residue via a cross-coupling reaction (Suzuki, Stille, or others).
• Cleavage of the protecting group on the amine: the necessity to protect the amino group in previous stages.

3.3. Detailed Synthetic Scheme

Based on the retrosynthetic analysis, the following 6-stage scheme for the synthesis of the target molecule is proposed (Scheme 1).

Stage 1: Protection of the Amino Group
The starting compound is sulfanilamide (4-aminobenzenesulfonamide, 1). The amino group must be protected to prevent its participation in subsequent electrophilic substitution and metalation reactions. Acylation to form an acetamide is the most appropriate, as this protecting group is stable under the conditions of subsequent reactions and can be easily removed by hydrolysis. Treatment of compound 1 with acetic anhydride in the presence of a base (e.g., pyridine) yields 4-acetamidobenzenesulfonamide (2).

Scheme 1. Synthesis of the target molecule 2-Ag-5-THC-4-aminobenzenesulfonamide

Stage 1: Amino group protection
1 (sulfanilamide) + (CH3CO)2O → 2 (4-acetamidobenzenesulfonamide)

Stage 2: Selective iodination at position 5
2 + I2 + [O] → 3 (5-iodo-4-acetamidobenzenesulfonamide)

Stage 3: Introduction of THC residue via Suzuki reaction
3 + THC-B(OH)2 + Pd(0) → 4 (5-THC-4-acetamidobenzenesulfonamide)

Stage 4: Ortho-metalation and introduction of silver atom
4 + strong base (e.g., LDA) → lithium-organic intermediate
Then + AgX (silver salt) → 5 (2-Ag-5-THC-4-acetamidobenzenesulfonamide)

Stage 5: Deprotection
5 + H3O+ (mild hydrolysis) → 6 (2-Ag-5-THC-4-aminobenzenesulfonamide)

Stage 2: Selective Iodination at Position 5
The next step is the introduction of an iodine atom at position 5 (meta-position to the amino group). The acetamido group is an ortho-para director, so direct electrophilic substitution could yield a mixture of isomers. To achieve selectivity, it is necessary to use sterically hindered iodinating agents or carry out the reaction under kinetic control. Alternatively, protection of the sulfonamide group could be used to block the para-position. Treatment of compound 2 with iodine in the presence of an oxidizing agent (e.g., sodium periodate) could yield 5-iodo-4-acetamidobenzenesulfonamide (3) with acceptable selectivity.

Stage 3: Introduction of the THC Residue via Cross-Coupling Reaction
The most challenging step is the formation of the C-C bond between the aromatic ring and the bulky THC residue. The Suzuki reaction is the most attractive, as it proceeds under mild conditions and is tolerant of many functional groups. For this, a boron derivative of THC is required – THC boronic acid (THC-B(OH)₂). Reaction of compound 3 with THC-B(OH)₂ in the presence of a palladium(0) catalyst and a base would yield 5-THC-4-acetamidobenzenesulfonamide (4).

Stage 4: Ortho-Metalation and Introduction of the Silver Atom
Introducing a silver atom directly into the aromatic ring is a non-trivial task. Classical electrophilic substitution reactions are not applicable here. A potential pathway is the use of ortho-metalation. The acetamido group is ortho-directing and can direct metalation to position 2. Treatment of compound 4 with a strong base (e.g., LDA – lithium diisopropylamide) at low temperature would lead to the formation of a lithium-organic intermediate at position 2. Subsequent addition of a silver salt (e.g., AgBr or AgOTf) could yield the target compound 5 (2-Ag-5-THC-4-acetamidobenzenesulfonamide). The stability of the C-Ag bond is a key issue, and this compound would likely be sensitive to light and moisture.

Stage 5: Deprotection
The final step is the removal of the acetyl protecting group from the amine. Mild acidic or basic hydrolysis would yield the target compound 6 with the free amino group necessary for antibacterial activity. The hydrolysis conditions must be sufficiently mild to avoid destroying the sensitive C-Ag and C-THC bonds.

3.4. Predicted Biological Effects

We predict that the hybrid molecule 2-Ag-5-THC-4-aminobenzenesulfonamide may exhibit three main types of biological activity:

1. Antibacterial Activity.
   • Sulfanilamide Mechanism: If the free para-amino group is preserved, the molecule could theoretically compete with PABA for the active site of the bacterial enzyme. However, the presence of bulky substituents on the ring (Ag, THC) could create steric hindrance for enzyme binding, potentially reducing or abolishing this type of activity. This is the main risk of the project.
   • Silver-Mediated Mechanism: Silver ions (Ag⁺) are potent antimicrobial agents. They can bind to bacterial proteins, disrupt cell membrane function, and interact with DNA. If the C-Ag bond is labile in vivo, the compound could act as a prodrug, releasing silver ions directly at the site of application, analogous to silver sulfadiazine.
2. Anti-inflammatory and Analgesic Activity.
   • Cannabinoid Mechanism: The THC residue, provided its conformational mobility is preserved, could bind to cannabinoid receptors CB1 (primarily in the CNS) and CB2 (primarily in the immune system). This would result in effects such as reduced inflammation, modulation of pain signals, and possibly immunosuppression.
   • Synergism: Combining an antibacterial component (sulfanilamide/Ag) and an anti-inflammatory component (THC) in one molecule is particularly valuable for treating infected wounds, where the inflammatory process is an integral part of the pathogenesis. Topical application of such an ointment could simultaneously combat infection and reduce pain and swelling.

3.5. Toxicological Aspects

When developing drugs based on silver compounds, potential nephrotoxicity must be considered. Metals, including silver, are among the substances capable of causing structural and functional kidney disorders. Toxic kidney damage can manifest as hematuria, proteinuria, oliguria, azotemia, and other symptoms. With topical application on limited surfaces, systemic absorption of silver is minimal, reducing the risk of nephrotoxicity. However, when applied to large wound surfaces, monitoring of renal function is necessary.

4. CONCLUSIONS

The theoretical justification for creating hybrid molecules based on sulfanilamide, silver, and THC indicates their significant, albeit hypothetical, potential as agents with combined (antibacterial and anti-inflammatory/analgesic) action.

The proposed 6-stage synthetic scheme includes key transformations: protection of the amino group by acylation, selective iodination, the Suzuki reaction for introducing the THC residue, ortho-metalation for introducing the silver atom, and final deprotection.

The main challenges are:

1. The extreme complexity of the synthesis and the need to optimize conditions at each stage.
2. The risk of losing key antibacterial activity due to modification of the benzene ring.
3. The stability of the C-Ag bond and the compound’s sensitivity to light and moisture.
4. Potential nephrotoxicity characteristic of silver compounds.

Experimental verification of this concept will require close collaboration between synthetic organic chemists, specialists in organometallic chemistry, and pharmacologists. Further research should focus on finding mild and selective methods for introducing the metal into the aromatic system, assessing the influence of substituents on the affinity of the sulfanilamide fragment for its bacterial target, and detailed toxicological profiling.

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