Prodrugs for amines

The role of the methoxy group in approved drugs

The methoxy substituent is prevalent in natural products and, consequently, is present in many natural product-derived drugs. It has also been installed in modern drug molecules with no remnant of natural product features because medicinal chemists have been taking advantage of the benefits that this small functional group can bestow on ligand-target binding, physicochemical properties, and ADME parameters. Herein, over 230 methoxy-containing small-molecule drugs, as well as several fluoromethoxy-containing drugs, are presented from the vantage point of the methoxy group. Biochemical mechanisms of action, medicinal chemistry SAR studies, and numerous X-ray cocrystal structures are analyzed to identify the precise role of the methoxy group for many of the drugs and drug classes. Although the methoxy substituent can be considered as the hybridization of a hydroxy and a methyl group, the combination of these functionalities often results in unique effects that can amount to more than the sum of the individual parts.

Discovery of a Long Half-Life AURKA Inhibitor to Treat MYC-Amplified Solid Tumors as a Monotherapy and in Combination with Everolimus

Aurora kinase inhibitors, such as alisertib, can destabilize MYC-family oncoproteins and have demonstrated compelling antitumor efficacy. In this study, we report 6K465, a novel pyrimidine-based Aurora A inhibitor, that reduces levels of c-MYC and N-MYC oncoproteins more potently than alisertib. In an analysis of the antiproliferative effect of 6K465, the sensitivities of small cell lung cancer (SCLC) and breast cancer cell lines to 6K465 were strongly associated with the protein levels of c-MYC and/or N-MYC. We also report DBPR728, an acyl-based prodrug of 6K465 bearing fewer hydrogen-bond donors, that exhibited 10-fold improved oral bioavailability. DBPR728 induced durable tumor regression of c-MYC- and/or N-MYC-overexpressing xenografts including SCLC, triple-negative breast cancer, hepatocellular carcinoma, and medulloblastoma using a 5-on-2-off or once-a-week dosing regimen on a 21-day cycle. A single oral dose of DBPR728 at 300 mg/kg induced c-MYC reduction and cell apoptosis in the tumor xenografts for more than 7 days. The inhibitory effect of DBPR728 at a reduced dosing frequency was attributed to its uniquely high tumor/plasma ratio (3.6-fold within 7 days) and the long tumor half-life of active moiety 6K465. Furthermore, DBPR728 was found to synergize with the mTOR inhibitor everolimus to suppress c-MYC- or N-MYC-driven SCLC. Collectively, these results suggest DBPR728 has the potential to treat cancers overexpressing c-MYC and/or N-MYC.

Prodrug Rewards in Medicinal Chemistry: An Advance and Challenges Approach for Drug Designing

This article emphasizes the importance of prodrugs and their diverse spectrum of effects in the field of developing novel drugs for a variety of biological applications. Prodrugs are chemicals that are supplied inactively, but then go through enzymatic and chemical transformation in vivo to release the active parent medication that can have the desired pharmacological effect. By adding an inactive chemical moiety, prodrugs are improved in a number of ways that contribute to their potency and durability. For the purpose of illustrating the usefulness of the prodrug approach, this review covers examples of prodrugs that have been made available or are now undergoing human trials. Additionally, it included lists of the most common functional groups, carrier linkers, and reactive chemicals that can be used to create prodrugs. The current study also provides a brief introduction, several chemical methods and modifications for creating prodrugs and mutual prodrugs, as well as an explanation of recent advancements and difficulties in the field of prodrug design. The primary chemical carriers employed in the creation of prodrugs, such as esters, amides, imides, NH-acidic carriers, amines, alcohols, carbonyl, carboxylic, and azo-linkages, are also discussed. This review also discusses glycosidic and triglyceride mutually activated prodrugs, which aim to deliver the drugs after bioconversion at the intended site of action. The article also discusses the extensive chemistry and wide variety of applications of recently approved prodrugs, such as antibacterial, anti-inflammatory, cardiovascular, antiplatelet, antihypertensive, atherosclerotic, antiviral, etc. In order to illustrate the prodrug and mutual drug concept's various applications and highlight its many triumphs in overcoming the formulation and delivery of problematic pharmaceuticals, this work represents a thorough guide that includes the synthetic moiety for the reader.

PAMAM-G4 protect the N-(2-hydroxyphenyl)-2-propylpentanamide (HO-AAVPA) and maintain its antiproliferative effects on MCF-7

Our work group designed and synthesized a promissory compound N-(2-hydroxyphenyl)-2-propylpentanamide (HO-AAVPA). The HO-AAVPA is a HDAC1 inhibitor and antiproliferative in cancer cell lines. However, HO-AAVPA is poor water solubility and enzymatically metabolized. In this work, the fourth-generation poly(amidoamine) dendrimer (PAMAM-G4) was used as a drug deliver carrier of HO-AAVPA. Moreover, HO-AAVPA and HO-AAVPA-PAMAM complex were submitted to forced degradation studies (heat, acid, base, oxidation and sunlight). Also, the HO-AAVPA-PAMAM-G4 complex was assayed as antiproliferative in a breast cancer cell line (MCF-7). The HO-AAVPA-PAMAM-G4 complex was obtained by docking and experimentally using three pH conditions: acid (pH = 3.0), neutral (pH = 7.0) and basic (pH = 9.0) showing that PAMAM-G4 captureand protect the HO-AAVPA from forced degradation, it is due to sunlight yielded a by-product from HO-AAVPA. In addition, the PAMAM-G4 favored the HO-AAVPA water solubility under basic and neutral pH conditions with significant difference (F_(2,18) = 259.9, p < 0.001) between the slopes of the three conditions being the basic condition which solubilizes the greatest amount of HO-AAVPA. Finally, the HO-AAVPA-PAMAM-G4 complex showed better antiproliferative effects on MCF-7 (IC₅₀ = 75.3 μM) than HO-AAVPA (IC₅₀ = 192 μM). These results evidence that PAMAM-G4 complex improve the biological effects of HO-AAVPA.

Isoform selectivities of novel 4-hydroxycoumarin imines as inhibitors of myosin II

Muscle myosin inhibition could be used to treat many medical conditions involving hypercontractile states, including muscle spasticity, chronic musculoskeletal pain, and hypertrophic cardiomyopathy. A series of 13 advanced analogs of 3-(N-butylethanimidoyl)ethyl)-4-hydroxy-2H-chromen-2-one (BHC) were synthesized to explore extended imine nitrogen side chains and compare aldimines vs. ketimines. None of the new analogs inhibit nonmuscle myosin in a cytokinesis assay. ATPase structure-activity relationships reveal that selectivity for cardiac vs. skeletal myosin can be tuned with subtle structural changes. None of the compounds inhibited smooth muscle myosin II. Docking the compounds to homology models of cardiac and skeletal myosin II gave rationales for the effects of side arm length on inhibition selectivity and for cardiac vs. skeletal myosin. Properties including solubility, stability and toxicity, suggest that certain BHC analogs may be useful as candidates for preclinical studies or as lead compounds for advanced candidates for drugs with cardiac or skeletal muscle myosin selectivity.

Anticancer activity and metabolic alteration in colon and prostate cancer cells by novel moxifloxacin conjugates with fatty acids

The positive and pro-economic trend in the management of cancer treatment is the search for the antineoplastic potential of known, widely used and safe drugs with a different clinical purpose. A good candidate seems to be moxifloxacin with broad-spectrum antibacterial activity, which as the member of the fourth generation fluoroquinolone is known to affect not only bacterial but also eukaryotic DNA topoisomerases, however at high concentration. Due to the fact that the modification of parent drug with lipid component can improve anticancer potential by increasing of bioavailability, selectivity, and cytotoxic efficiency, we evaluated the mechanisms of cytotoxic activity of novel moxifloxacin conjugates with fatty acids and verified metabolic profile in SW480, SW620 and PC3 cell lines. Our study revealed that cytotoxic potential of moxifloxacin conjugates was stronger than free moxifloxacin, moreover, they remained non-toxic to normal HaCaT cells. PC3 were more sensitive to MXF conjugates than colon cancer cells. The most promising cytotoxic activity exhibited conjugate 4m and 16m with oleic and stearic acid reducing viability of PC3 and SW620 cells. Tested conjugates activated caspases 3/7 and induced late-apoptosis, mainly in PC3 and SW620 cells. However, the most pronounced inhibition of NF-κB activation and IL-6 secretion was observed in SW480. Metabolomic analysis indicated influence of the moxifloxacin conjugates on intensity of lipid derivatives with the most successful metabolite profile in PC3. Our findings suggested the cytotoxic potential of moxifloxacin conjugates, especially with oleic and stearic acid can be beneficial in oncological therapy, including their possible anti-inflammatory and known antibacterial effect.

Magnetically Separable Visible Light-Active Ag0.75Ni0.25 Binary Alloy Nanoparticles as a Highly Efficient Photocatalyst for the Selective Oxidative Coupling of Aniline to Azobenzene

Aniline wastes can be converted to useful pharmaceutical and industrial compounds like azobenzene. For this purpose, a bimetallic Ag_0.75Ni_0.25 alloy is designed in the nanoscale range resembling a fivefold twinned morphology using water as the solvent. These newly developed alloy nanoparticles (NPs) are employed for the first time as an efficient visible light-active photocatalyst for the oxidative homocoupling of aniline to azobenzene. Our catalytic protocol is highly sustainable for a large number of aniline substrates with a high yield of the product (up to 95%), which might be attributed to the combinational and superior properties achieved on alloy formation in comparison to the monometallic counterparts. High-electron density amines (p-anisidine) display greater photocatalytic proficiency than that of low-electron density amines (4-fluoroaniline). The developed photocatalyst is magnetically well-separable and can be reused for at least five catalytic cycles without appreciable loss in its activity.

Aminopeptidase B can bioconvert L-type amino acid transporter 1 (LAT1)-utilizing amide prodrugs in the brain

A prodrug approach is a powerful method to temporarily change the physicochemical and thus, pharmacokinetic properties of drugs. However, in site-selective targeted prodrug delivery, tissue or cell-specific bioconverting enzyme is needed to be utilized to release the active parent drug at a particular location. Unfortunately, ubiquitously expressed enzymes, such as phosphatases and carboxylesterases are well used in phosphate and ester prodrug applications, but less is known about enzymes selectively expressed, e.g., in the brain and enzymes that can hydrolyze more stable prodrug bonds, such as amides and carbamates. In the present study, L-type amino acid transporter 1 (LAT1)-utilizing amide prodrugs bioconverting enzyme was identified by gradually exploring the environment and possible determinants, such as pH and metal ions, that affect amide prodrug hydrolysis. Based on inducement by cobalt ions and slightly elevated pH (8.5) as well as localization in plasma, liver, and particularly in the brain, aminopeptidase B was proposed to be responsible for the bioconversion of the majority of the studied amino acid amide prodrugs. However, this enzyme hydrolyzed only those prodrugs that contained an aromatic promoiety (L-Phe), while leaving the aliphatic promoeities (L-Lys) and the smallest prodrug (with L-Phe promoiety) intact. Moreover, the parent drugs’ structure (flexibility and the number of aromatic rings) largely affected the bioconversion rate. It was also noticed in this study, that there were species differences in the bioconversion rate by aminopeptidase B (rodents > human), although the in vitro–in vivo correlation of the studied prodrugs was relatively accurate.

HPMA Copolymer Mebendazole Conjugate Allows Systemic Administration and Possesses Antitumour Activity In Vivo

Mebendazole and other benzimidazole antihelmintics, such as albendazole, fenbendazole, or flubendazole, have been shown to possess antitumour activity, primarily due to their microtubule-disrupting activity. However, the extremely poor water-solubility of mebendazole and other benzimidazoles, resulting in very low bioavailability, is a serious drawback of this class of drugs. Thus, the investigation of their antitumour potential has been limited so far to administering repeated high doses given peroral (p.o.) or to using formulations, such as liposomes. Herein, we report a fully biocompatible, water-soluble, HPMA copolymer-based conjugate bearing mebendazole (P-MBZ; M_w 28–33 kDa) covalently attached through a biodegradable bond, enabling systemic administration. Such an approach not only dramatically improves mebendazole solubility but also significantly prolongs the half-life and ensures tumour accumulation via an enhanced permeation and retention (EPR) effect in vivo. This P-MBZ has remarkable cytostatic and cytotoxic activities in EL-4 T-cell lymphoma, LL2 lung carcinoma, and CT-26 colon carcinoma mouse cell lines in vitro, with corresponding IC₅₀ values of 1.07, 1.51, and 0.814 µM, respectively. P-MBZ also demonstrated considerable antitumour activity in EL-4 tumour-bearing mice when administered intraperitoneal (i.p.), either as a single dose or using 3 intermittent doses. The combination of P-MBZ with immunotherapy based on complexes of IL-2 and anti-IL-2 mAb S4B6, potently stimulating activated and memory CD8⁺ T cells, as well as NK cells, further improved the therapeutic effect.

Multifunctional Lipid Bilayer Nanocarriers for Cancer Immunotherapy in Heterogeneous Tumor Microenvironments, Combining Immunogenic Cell Death Stimuli with Immune Modulatory Drugs

In addition to the contribution of cancer cells, the solid tumor microenvironment (TME) has a critical role in determining tumor expansion, antitumor immunity, and the response to immunotherapy. Understanding the details of the complex interplay between cancer cells and components of the TME provides an unprecedented opportunity to explore combination therapy for intervening in the immune landscape to improve immunotherapy outcome. One approach is the introduction of multifunctional nanocarriers, capable of delivering drug combinations that provide immunogenic stimuli for improvement of tumor antigen presentation, contemporaneous with the delivery of coformulated drug or synthetic molecules that provide immune danger signals or interfere in immune-escape, immune-suppressive, and T-cell exclusion pathways. This forward-looking review will discuss the use of lipid-bilayer-encapsulated liposomes and mesoporous silica nanoparticles for combination immunotherapy of the heterogeneous immune landscapes in pancreatic ductal adenocarcinoma and triple-negative breast cancer. We describe how the combination of remote drug loading and lipid bilayer encapsulation is used for the synthesis of synergistic drug combinations that induce immunogenic cell death, interfere in the PD-1/PD-L1 axis, inhibit the indoleamine-pyrrole 2,3-dioxygenase (IDO-1) immune metabolic pathway, restore spatial access to activated T-cells to the cancer site, or reduce the impact of immunosuppressive stromal components. We show how an integration of current knowledge and future discovery can be used for a rational approach to nanoenabled cancer immunotherapy.

A New Amino Acid for Improving Permeability and Solubility in Macrocyclic Peptides through Side Chain-to-Backbone Hydrogen Bonding

Despite the notoriously poor membrane permeability of peptides, many cyclic peptide natural products show high passive membrane permeability and potently inhibit a variety of "undruggable" intracellular targets. A major impediment to the design of cyclic peptides with good permeability is the high desolvation energy associated with the peptide backbone amide NH groups. While several strategies have been proposed to mitigate this deleterious effect, only few studies have used polar side chains to sequester backbone NH groups. We investigated the ability of N,N-pyrrolidinylglutamine (Pye), whose side chain contains a powerful hydrogen-bond-accepting C═O amide group but no hydrogen-bond donors, to sequester exposed backbone NH groups in a series of cyclic hexapeptide diastereomers. Analyses revealed that specific Leu-to-Pye substitutions conferred dramatic improvements in aqueous solubility and permeability in a scaffold- and position-dependent manner. Therefore, this approach offers a complementary tool for improving membrane permeability and solubility in cyclic peptides.

Synthesis of Substituted -N-(5-((7-Methyl-2-Oxo-2H-Chromen-4-yl)- Methyl)-1,3,4-Thiadiazol-2-yl)-Benzamide Derivatives Using TBTU as Coupling Agent and their Evaluation for Anti Tubercular Activity

Abstract:

Tuberculosis remains a highly infectious disease across the world. In the identification of new antitubercular agents, coumarin clubbed thiadiazole amides have been synthesized and evaluated for in vitro antitubercular activity. Owing to the growing concern of chemicals and their impact on the environment, greener and faster reaction conditions needed to be incorporated. Therefore, we used TBTU as a coupling reagent for efficient and facile synthesis of substituted-N-(5-((7-methyl-2-oxo-2Hchromes- 4-yl)-methyl)-1,3, 4-thiadiazol-2-yl)-benzamide 4a-j with good yields up to 95% in mild reaction conditions. All the synthesized compounds were evaluated in vitro for anti-tubercular activity against the H37Rv strain of M. tuberculosis. Compounds 4c, 4d, and 4f were found active at 12.5 μg/mL against M. tb H37Rv. Electron withdrawing substituents present on aromatic side chains showed promising anti-tubercular activity.

The Effect of Fatty Acids on Ciprofloxacin Cytotoxic Activity in Prostate Cancer Cell Lines. Does Lipid Component Enhance Anticancer Ciprofloxacin Potential?

Simple Summary

Most prostate cancers are initially hormone-dependent but later gain a hormone-independent phenotype associated with changes in lipid metabolism, including enhanced absorption of extracellular fatty acids. The aim of our study was to assess the effect of ciprofloxacin conjugates with fatty acids on different type of prostate cancer (LNCaP and DU-145) and normal (RWPE-1) cells, as well as their influence on cell lipid metabolism by proteomic analysis. All tested conjugates exhibited cytotoxic potential, the most powerful for oleic, elaidic and docosahexaenoic acids. The hormone-independent DU145 line was more sensitive to derivatives than the hormone-dependent LNCaP line. These results are consistent with previously observed pronounced cytotoxic effect of conjugates on a hormone-insensitive PC3 line. Tested derivatives decreased intensity of proteins involved in prostate cancer lipid metabolism. Our findings confirm the involvement of lipid metabolism in prostate carcinogenesis indicating a target for fatty acids as drug carriers.

Abstract

Purpose: To assess cytotoxic effect of ciprofloxacin conjugates with fatty acids on prostate cancer cells (LNCaP and DU-145) with different hormone sensitivity, based on previous promising results from the PC3 cells. Methods: Cytotoxicity were estimated using MTT and LDH tests, whereas its mechanisms were estimated by apoptosis and IL-6 assays. The intensity of proteins involved in lipid metabolism was determined using ML-CS assay. Results: The hormone insensitive DU-145 cells were more vulnerable than the hormone sensitive LNCaP cells. The IC50 values for oleic (4), elaidic (5) and docosahexaenoic acid (8) conjugates were 20.2 µM, 17.8 µM and 16.5 µM, respectively, in DU-145 cells, whereas in LNCaP cells IC50 exceeded 20 µM. The strong conjugate cytotoxicity was confirmed in the LDH test, the highest (70.8%) for compound (5) and 64.2% for compound (8) in DU-145 cells. This effect was weaker for LNCaP cells (around 60%). The cytotoxic effect of unconjugated ciprofloxacin and fatty acids was weaker. The early apoptosis was predominant in LNCaP while in DU-145 cells both early and late apoptosis was induced. The tested conjugates decreased IL-6 release in both cancer cell lines by almost 50%. Proteomic analysis indicated influence of the ciprofloxacin conjugates on lipid metabolic proteins in prostatic cancer. Conclusion: Our findings suggested the cytotoxic potential of ciprofloxacin conjugates with reduction in proteins involved in prostate cancer progress.

Recent progress in the chemistry of β-aminoketones

The current study highlighted the significance of β-aminoketones as privileged biologically active molecules, recent synthetic strategies, and synthetic applications.

The cleavage kinetics of hydrazide derivatives of isoniazid by HPLC-UV/DAD and its impact on activity against Mycobacterium tuberculosis

Isoniazid is a first-line drug for the treatment of tuberculosis, a bacterial disease caused by Mycobacterium tuberculosis. Its terminal amino group is highly reactive, leading to significant metabolic deactivation, drug interactions and hepatotoxicity. It is speculated that the activity of isoniazid derivatives is, in part, related to the cleavage of the protecting group. Therefore, this study aimed to evaluate the cleavage characteristics of previously developed isoniazid derivatives through kinetic studies by high-performance liquid chromatography with ultraviolet-diode array detectio to establish a comparison between the rates of the process and the respective activities against M. tuberculosis. Chromatographic separations were performed on an XDB C18 column coupled to an XDB C18 precolumn. The mobile phase consisted of ultrapure water and acetonitrile in gradient mode. The flow rate was 1.0 mL/min, the injection volume was 20 μL, and the detection wavelengths were 230 nm (derivatives and isatins) and 270 nm (isoniazid). Incubation of derivatives was carried out for 5 days in 10 mmol/L phosphate buffer solution (pH 3.0, 7.4, 8.0) or in fetal bovine serum at 37 °C. The incubation reduced the concentration of the derivatives and led to the formation of isoniazid in a first-order kinetic reaction. Isoniazid formation was logarithmically correlated with the minimum inhibitory concentration of the derivatives. The results showed that higher cleavage rates are associated with greater activities against M. tuberculosis, providing important information for the development of future generations of isoniazid derivatives and for screening drug candidates for the treatment of tuberculosis.

Inulin and Its Application in Drug Delivery

Inulin’s unique and flexible structure, stabilization/protective effects, and organ targeting ability make it an excellent drug delivery carrier compared to other biodegradable polysaccharides. The three hydroxyl groups attached to each fructose unit serve as an anchor for chemical modification. This, in turn, helps in increasing bioavailability, improving cellular uptake, and achieving targeted, sustained, and controlled release of drugs and biomolecules. This review focuses on the various types of inulin drug delivery systems such as hydrogel, conjugates, nanoparticles, microparticles, micelles, liposomes, complexes, prodrugs, and solid dispersion. The preparation and applications of the different inulin drug delivery systems are further discussed. This work highlights the fact that modification of inulin allows the use of this polymer as multifunctional scaffolds for different drug delivery systems.

Phosphate-Based Self-Immolative Linkers for the Delivery of Amine-Containing Drugs

Amine-containing drugs often show poor pharmacological properties, but these disadvantages can be overcome by using a prodrug approach involving self-immolative linkers. Accordingly, we designed l-lactate linkers as ideal candidates for amine delivery. Furthermore, we designed linkers bearing two different cargos (aniline and phenol) for preferential amine cargo release within 15 min. Since the linkers carrying secondary amine cargo showed high stability at physiological pH, we used our strategy to prepare phosphate-based prodrugs of the antibiotic Ciprofloxacin. Therefore, our study will facilitate the rational design of new and more effective drug delivery systems for amine-containing drugs.

HPMA-Based Polymer Conjugates for Repurposed Drug Mebendazole and Other Imidazole-Based Therapeutics

Recently, the antitumor potential of benzimidazole anthelmintics, such as mebendazole and its analogues, have been reported to have minimal side effects, in addition to their well-known anti-parasitic abilities. However, their administration is strongly limited owing to their extremely poor solubility, which highly depletes their overall bioavailability. This study describes the design, synthesis, and physico-chemical properties of polymer-mebendazole nanomedicines for drug repurposing in cancer therapy. The conjugation of mebendazole to water-soluble and biocompatible polymer carrier was carried out via biodegradable bond, relying on the hydrolytic action of lysosomal hydrolases for mebendazole release inside the tumor cells. Five low-molecular-weight mebendazole derivatives, differing in their inner structure, and two polymer conjugates differing in their linker structure, were synthesized. The overall synthetic strategy was designed to enable the modification and polymer conjugation of most benzimidazole-based anthelmintics, such as albendazole, fenbendazole or albendazole, besides the mebendazole. Furthermore, the described methodology may be suitable for conjugation of other biologically active compounds with a heterocyclic N-H group in their molecules.

Transition Metal Catalyzed Free-Amine (-NH2 ) Directed C-H Bond Activation and Functionalization for Biaryl Frameworks

Transition-metal-catalyzed direct transformation of inert C-H bond has revolutionized the arsenal of main-stream organic synthesis, providing a new upfront to forge structurally enriched and biologically relevant scaffolds in a step- and atom-economical way. Past decades have accounted for the major developments in this realm, proclaiming excellent site-selectivity by exploiting a variety of coordinating directing groups (DGs). Consideration of versatile, abundant, sp³ -hybridized free-amine (-NH₂ ) functionality for the same purpose has always been a formidable task owing to its innate reactivity. In recent years, free-amine functionality has emerged as a potent DG for a wide range of C-C and C-heteroatom bonds formations and annulation cascades. In this review article, we have discussed the advancements of free-amine directed C-H activation/functionalization reactions towards biaryl frameworks made within a decade (2012 to 2021).

Enzyme Models-From Catalysis to Prodrugs

Enzymes are highly specific biological catalysts that accelerate the rate of chemical reactions within the cell. Our knowledge of how enzymes work remains incomplete. Computational methodologies such as molecular mechanics (MM) and quantum mechanical (QM) methods play an important role in elucidating the detailed mechanisms of enzymatic reactions where experimental research measurements are not possible. Theories invoked by a variety of scientists indicate that enzymes work as structural scaffolds that serve to bring together and orient the reactants so that the reaction can proceed with minimum energy. Enzyme models can be utilized for mimicking enzyme catalysis and the development of novel prodrugs. Prodrugs are used to enhance the pharmacokinetics of drugs; classical prodrug approaches focus on alternating the physicochemical properties, while chemical modern approaches are based on the knowledge gained from the chemistry of enzyme models and correlations between experimental and calculated rate values of intramolecular processes (enzyme models). A large number of prodrugs have been designed and developed to improve the effectiveness and pharmacokinetics of commonly used drugs, such as anti-Parkinson (dopamine), antiviral (acyclovir), antimalarial (atovaquone), anticancer (azanucleosides), antifibrinolytic (tranexamic acid), antihyperlipidemia (statins), vasoconstrictors (phenylephrine), antihypertension (atenolol), antibacterial agents (amoxicillin, cephalexin, and cefuroxime axetil), paracetamol, and guaifenesin. This article describes the works done on enzyme models and the computational methods used to understand enzyme catalysis and to help in the development of efficient prodrugs.

Synthesis, Characterization, and DFT Studies of N-(3,5-Bis(trifluoromethyl)benzyl)stearamide

The novel N-(3,5-bis(trifluoromethyl)benzyl)stearamide 3 was prepared in moderate yield by a solventless direct amidation reaction of stearic acid 1 with 3,5-bis(trifluoromethyl)benzylamine 2 at 140 °C for 24 h under metal- and catalyst-free conditions. This practical method was conducted in air without any special treatment or activation. The fatty acid amide 3 was fully characterized by IR, UV–Vis, 1D and 2D NMR spectroscopy, mass spectrometry, and elemental analysis. Moreover, molecular electrostatic potential studies, determination of quantum descriptors, fundamental vibrational frequencies, and intensity of vibrational bands were computed by density functional theory (DFT) using the B3LYP method with 6-311+G(d,p) basis set in gas phase. Simulation of the infrared spectrum using the results of these calculations led to good agreement with the observed spectral patterns.

Recent advances in prodrug-based nanoparticle therapeutics

Extensive research into prodrug modification of active pharmaceutical ingredients and nanoparticle drug delivery systems has led to unprecedented levels of control over the pharmacological properties of drugs and resulted in the approval of many prodrug or nanoparticle-based therapies. In recent years, the combination of these two strategies into prodrug-based nanoparticle drug delivery systems (PNDDS) has been explored as a way to further advance nanomedicine and identify novel therapies for difficult-to-treat indications. Many of the PNDDS currently in the clinical development pipeline are expected to enter the market in the coming years, making the rapidly evolving field of PNDDS highly relevant to pharmaceutical scientists. This review paper is intended to introduce PNDDS to the novice reader while also updating those working in the field with a comprehensive summary of recent efforts. To that end, first, an overview of FDA-approved prodrugs is provided to familiarize the reader with their advantages over traditional small molecule drugs and to describe the chemistries that can be used to create them. Because this article is part of a themed issue on nanoparticles, only a brief introduction to nanoparticle-based drug delivery systems is provided summarizing their successful application and unfulfilled opportunities. Finally, the review's centerpiece is a detailed discussion of rationally designed PNDDS formulations in development that successfully leverage the strengths of prodrug and nanoparticle approaches to yield highly effective therapeutic options for the treatment of many diseases.

Selenoxide Elimination Triggers Enamine Hydrolysis to Primary and Secondary Amines: A Combined Experimental and Theoretical Investigation

We discuss a novel selenium-based reaction mechanism consisting in a selenoxide elimination-triggered enamine hydrolysis. This one-pot model reaction was studied for a set of substrates. Under oxidative conditions, we observed and characterized the formation of primary and secondary amines as elimination products of such compounds, paving the way for a novel strategy to selectively release bioactive molecules. The underlying mechanism was investigated using NMR, mass spectrometry and density functional theory (DFT).

Metabolic N-Dealkylation and N-Oxidation as Elucidators of the Role of Alkylamino Moieties in Drugs Acting at Various Receptors

Metabolic reactions that occur at alkylamino moieties may provide insight into the roles of these moieties when they are parts of drug molecules that act at different receptors. N-dealkylation of N,N-dialkylamino moieties has been associated with retaining, attenuation or loss of pharmacologic activities of metabolites compared to their parent drugs. Further, N-dealkylation has resulted in clinically used drugs, activation of prodrugs, change of receptor selectivity, and providing potential for developing fully-fledged drugs. While both secondary and tertiary alkylamino moieties (open chain aliphatic or heterocyclic) are metabolized by CYP450 isozymes oxidative N-dealkylation, only tertiary alkylamino moieties are subject to metabolic N-oxidation by Flavin-containing monooxygenase (FMO) to give N-oxide products. In this review, two aspects will be examined after surveying the metabolism of representative alkylamino-moieties-containing drugs that act at various receptors (i) the pharmacologic activities and relevant physicochemical properties (basicity and polarity) of the metabolites with respect to their parent drugs and (ii) the role of alkylamino moieties on the molecular docking of drugs in receptors. Such information is illuminative in structure-based drug design considering that fully-fledged metabolite drugs and metabolite prodrugs have been, respectively, developed from N-desalkyl and N-oxide metabolites.

Aldsulfin, a novel unusual anti-mannheimiosis epithiodiketopiperazine antibiotic produced by Lasiodiplodia pseudotheobromae FKI-4499

An anti-mannheimiosis agent, aldsulfin, was isolated from a culture broth of the fungus Lasiodiplodia pseudotheobromae FKI-4499, together with a known compound, lasiodipline C, using bioassay-guided fractionation. Spectroscopic analysis of aldsulfin, using NMR, mass spectrometry, and CD analyses revealed it to be an epithiodiketopiperazine with an unstable and unusual hemithioaminal moiety. Aldsulfin showed antibacterial activity against Mannheimia haemolytica and Pasteurella multocida.

Highly economical and direct amination of sp3 carbon using low-cost nickel pincer catalyst

Developing more efficient routes to achieve C-N bond coupling is of great importance to industries ranging from products in pharmaceuticals and fertilizers to biomedical technologies and next-generation electroactive materials. Over the past decade, improvements in catalyst design have moved synthesis away from expensive metals to newer inexpensive C-N cross-coupling approaches via direct amine alkylation. For the first time, we report the use of an amide-based nickel pincer catalyst (1) for direct alkylation of amines via activation of sp3 C-H bonds. The reaction was accomplished using a 0.2 mol% catalyst and no additional activating agents other than the base. Upon optimization, it was determined that the ideal reaction conditions involved solvent dimethyl sulfoxide at 110 °C for 3 h. The catalyst demonstrated excellent reactivity in the formation of various imines, intramolecularly cyclized amines, and substituted amines with a turnover number (TON) as high as 183. Depending on the base used for the reaction and the starting amines, the catalyst demonstrated high selectivity towards the product formation. The exploration into the mechanism and kinetics of the reaction pathway suggested the C-H activation as the rate-limiting step, with the reaction second-order overall, holding first-order behavior towards the catalyst and toluene substrate.

Fluoroquinolone-3-carboxamide Amino Acid Conjugates: Synthesis, Antibacterial Properties And Molecular Modeling Studies

Background:

Bacterial infections are considered as one of the major global health threats, so it is very essential to design and develop new antibacterial agents to overcome the drawbacks of existing antibacterial agents.

Method:

The aim of this work is to synthesize a series of new fluoroquinolone-3-carboxamide amino acid conjugates by molecular hybridization. We utilized benzotriazole chemistry to synthesize the desired hybrid conjugates.

Result:

All the conjugates were synthesized in good yields, characterized, evaluated for their antibacterial activity. The compounds were screened for their antibacterial activity using methods adapted from the Clinical and Laboratory Standards Institute. Synthesized conjugates were tested for activity against medically relevant pathogens; Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27856) Staphylococcus aureus (ATCC 25923) and Enterococcus faecalis (ATCC 19433).

Conclusion:

The observed antibacterial experimental data indicates the selectivity of our synthesized conjugates against E.Coli. The protecting group on amino acids decreases the antibacterial activity. The synthesized conjugates are non-toxic to the normal cell lines. The experimental data were supported by computational studies.

Direct Oxidative Azo Coupling of Anilines Using a Self-Assembled Flower-like CuCo2O4 Material as a Catalyst under Aerobic Conditions

Herein, we report the synthesis of a self-assembled flower-like CuCo₂O₄ material by the oxalate decomposition method. The crystalline structure and morphology of the material have been analyzed by powder X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray measurement techniques. The self-assembled flower-like CuCo₂O₄ material showed remarkable catalytic activity in the direct aerobic oxidative azo coupling of anilines under oxidant and other additive-free reaction conditions. The mechanistic insight of CuCo₂O₄ in the oxidative azo coupling reaction has been established by density functional theory calculations, which disclosed that the absorption and dissociation of areal oxygen preferentially take place at the Cu site and dissociation of aniline takes place at the Co site. Thus, the Cu and Co sites of CuCo₂O₄ exert a cooperative effect on the direct oxidative azo coupling reactions through the selective activation of anilines and aerobic oxygen. The CuCo₂O₄ material was recovered from the reaction mixture and reused for at least eight runs without appreciable loss of catalytic activity.

Improving Membrane Permeation in the Beyond Rule-of-Five Space by Using Prodrugs to Mask Hydrogen Bond Donors

A wide range of drug targets can be effectively modulated by peptides and macrocycles. Unfortunately, the size and polarity of these compounds prevents them from crossing the cell membrane to reach target sites in the cell cytosol. As such, these compounds do not conform to standard measures of drug-likeness and exist in beyond the rule-of-five space. In this work, we investigate whether prodrug moieties that mask hydrogen bond donors can be applied in the beyond rule-of-five domain to improve the permeation of macrocyclic compounds. Using a cyclic peptide model, we show that masking hydrogen bond donors in the natural polar amino acid residues (His, Ser, Gln, Asn, Glu, Asp, Lys, and Arg) imparts membrane permeability to the otherwise impermeable parent molecules, even though the addition of the masking group increases the overall compound molecular weight and the number of hydrogen bond acceptors. We demonstrate this strategy in PAMPA and Caco2 membrane permeability assays and show that masking with groups that reduce the number of hydrogen-bond donors at the cost of additional mass and hydrogen bond acceptors, a donor-acceptor swap, is effective.

Microwave-assisted One-pot Synthesis of Amide Bond using WEB

Background:

Amide bond plays a key role in medicinal chemistry, and the analysis of bioactive molecular database revealed that the carboxamide group appears in more than 25% of the existing database drugs. Typically amide bonds are formed from the union of carboxylic acid and amine; however, the product formation does not occur spontaneously. Several synthetic methods have been reported for amide bond formation in literature. Present work demonstrated simple and eco-friendly amide bond formation using carboxylic acid and primary amines through in situ generation of O-acylurea. The reaction was found to be more efficient, faster reaction rate; simple work-up gave pure compound isolation in moderate to excellent yield using microwave irradiation as compared to conventional heating.

Methods:

Developed one-pot synthesis of amide compounds using agro-waste derived greener catalyst under microwave irradiation.

Results:

Twenty amide bond containing organic compounds are synthesized from carboxylic acid with primary amine catalyzed by agro-waste derived medium under microwave irradiation. First, the reaction involved carboxylic acid activation using EDC.HCl, which is the required base for the neutralization and coupling. The method employed natural agro-waste derived from banana peel ash (WEB) for the coupling gave target amide product without the use of an external organic or inorganic base.

Conclusion:

In the present work, we demonstrated that agro-waste extract is an alternative greener catalytic medium for the condensation of organic carboxylic acid and primary amine under microwave irradiation. The method found several advantages compared to reported methods like solventfree, non-toxic, cheaper catalyst, and simple reaction condition. The final isolated product achieved chromatographically pure by simple recrystallization and did not require further purification.

Probing structural requirements for human topoisomerase I inhibition by a novel N1-Biphenyl fluoroquinolone

Fluoroquinolones substituted with N-1 biphenyl and napthyl groups were discovered to act as catalytically inhibitors of human topoisomerases I and II, and to possess anti-proliferative activity in vivo. Structural requirements for these novel quinolones to inhibit catalytic activity of human topoisomerase I have not been explored. In this work novel derivatives of the N-1 biphenyl fluoroquinolone were designed, synthesized and evaluated to understand structural requirements of the C-3 carboxylic acid, C-6 fluorine, C-7 aminomethylpyrrolidine, C-8 methoxy, and the N-1 biphenyl functional groups for hTopoI inhibition. Characterization of each analog for inhibition of hTopoI catalytic inhibition reveals critical insight into structural requirements of these novel quinolones for activity. Additionally, results of DNA binding and modeling studies suggest that N-1 biphenyl fluoroquinolones intercalate between the DNA base pairs with the N-1 biphenyl functional group, rather than the quinolone core, and that this mode of DNA intercalation contributes to inhibition of hTopoI by these novel structures. The results presented here support further development and evaluation of N-1 biphenyl fluoroquinolone analogs as a novel class of anti-cancer agents that act through catalytic inhibition of hTopoI.

The importance of evaluating the chemical structures and strategies to avoid pitfalls in quantitative bioanalysis

Quantitative bioanalytical data are crucial in pharmaceutical research and development, allowing project teams to make informed scientific decisions on the progression of candidate molecules to medicines. Many challenges are often encountered during the bioanalysis of drugs in biological matrices which require resolution in a timely manner. In this publication, guidance is provided to bioanalytical scientists on how to identify potential problems before they become an obstacle for the drug development and to share our experiences dealing some of most common problems encountered in the bioanalytical laboratory. Relevant topics in bioanalysis such as stabilization approaches for glucuronides (Acyl and N-); prodrugs (phosphate and esters), amides, amines, N-oxides; bioanalysis of light sensitive molecules, halogenated drugs and lactones are discussed in this publication.

Enhancing Oral Bioavailability of Cyclic RGD Hexa-peptides by the Lipophilic Prodrug Charge Masking Approach: Redirection of Peptide Intestinal Permeability from a Paracellular to Transcellular Pathway

Hydrophilic peptides constitute most of the active peptides. They mostly permeate via tight junctions (paracellular pathway) in the intestine. This permeability mechanism restricts the magnitude of their oral absorption and bioavailability. We hypothesized that concealing the hydrophilic residues of the peptide using the lipophilic prodrug charge masking approach (LPCM) can improve the bioavailability of hydrophilic peptides. To test this hypothesis, a cyclic N-methylated hexapeptide containing Arg-Gly-Asp (RGD) and its prodrug derivatives, masking the Arg and Asp charged side chains, were synthesized. The library was evaluated for intestinal permeability in vitro using the Caco-2 model. Further investigation of metabolic stability ex vivo models in rat plasma, brush border membrane vesicles (BBMVs), and isolated CYP3A4 microsomes and pharmacokinetic studies was performed on a selected peptide and its prodrug (peptide 12). The parent drug analogues were found to have a low permeability rate in vitro, corresponding to atenolol, a marker for paracellular permeability. Moreover, palmitoyl carnitine increased the P_app of peptide 12 by 4-fold, indicating paracellular permeability. The P_app of the prodrug derivatives was much higher than that of their parent peptides. For instance, the P_app of the prodrug 12P was 20-fold higher than the P_app of peptide 12 in the apical to basolateral (AB) direction. Whereas the permeability in the opposite direction (BA of the Caco-2 model) was significantly faster than the P_app AB, indicating the involvement of an efflux system. These results were corroborated when verapamil, a P-gp inhibitor, was added to the Caco-2 model and increased the P_app AB of prodrug 12P by 3-fold. The prodrug 12P was stable in the BBMVs environment, yet degraded quickly (less than 5 min) in the plasma into the parent peptide 12. Pharmacokinetic studies in rats showed an increase in the bioavailability of peptide 12 > 70-fold (from 0.58 ± 0.11% to 43.8 ± 14.9%) after applying the LPCM method to peptide 12 and converting it to the prodrug 12P. To conclude, the LPCM approach converted the absorption mechanism of the polar peptides from a paracellular to transcellular pathway that tremendously affects their oral bioavailability. The LPCM method provides a solution for the poor bioavailability of RGD cyclohexapeptides and paves the way for other active hydrophilic and charged peptides with poor oral bioavailability.

New hydrazides derivatives of isoniazid against Mycobacterium tuberculosis: Higher potency and lower hepatocytotoxicity

Tuberculosis (TB) is one of the leading causes of death worldwide. The emergence of multi-drug resistant strains of Mycobacterium tuberculosis (Mtb) and TB-HIV co-infection are major public health challenges. The anti-TB drugs of first choice were developed more than 4 decades ago and present several adverse effects, making the treatment of TB even more complicated and the development of new chemotherapeutics for this disease imperative. In this work, we synthesized two series of new acylhydrazides and evaluated their activity against different strains of Mtb. Derivatives of isoniazid (INH) showed important anti-Mtb activity, some being more potent than all anti-TB drugs of first choice. Moreover, three compounds proved to be more potent than INH against resistant Mtb. The Ames test showed favorable results for two of these substances compared to INH, one of which presented expressly lower toxicity to HepG2 cells than that of INH. This result shows that this compound has the potential to overcome one of the main adverse effects of this drug.

Cross-Coupling of Primary Amides to Aryl and Heteroaryl Partners Using (DiMeIHeptCl)Pd Promoted by Trialkylboranes or B(C6F5)3

Boron-derived Lewis acids have been shown to effectively promote the coupling of amide nucleophiles to a wide variety of oxidative addition partners using Pd-NHC catalysts. Through a combination of NMR spectroscopy and control studies with and without oxygen and radical scavengers, we propose that boron-imidates form under the basic reaction conditions that aid coordination of nitrogen to Pd(II), which is rate limiting, and directly delivers the intermediate for reductive elimination.

Self-assembling prodrugs

Covalent modification of therapeutic compounds is a clinically proven strategy to devise prodrugs with enhanced treatment efficacies. This prodrug strategy relies on the modified drugs that possess advantageous pharmacokinetic properties and administration routes over their parent drug. Self-assembling prodrugs represent an emerging class of therapeutic agents capable of spontaneously associating into well-defined supramolecular nanostructures in aqueous solutions. The self-assembly of prodrugs expands the functional space of conventional prodrug design, affording a possible pathway to more effective therapies as the assembled nanostructure possesses distinct physicochemical properties and interaction potentials that can be tailored to specific administration routes and disease treatment. In this review, we will discuss the various types of self-assembling prodrugs in development, providing an overview of the methods used to control their structure and function and, ultimately, our perspective on their current and future potential.

New amino acid-Schiff base derived from s-allyl cysteine and methionine alleviates carbon tetrachloride-induced liver dysfunction

In spite of the tremendous stride in modern medicine, conventional drugs used in the hepatotoxic management are mostly inadequate. The present study aims in the synthesis of novel Schiff base compound derived using s-allyl cystiene and methionine. The newly synthesized compound, 2-((2-((2-(allylthio)-1-carboxyethyl)imino)ethylidene)amino)-4-(methylthio)butanoic acid (ACEMB) was characterized using UV-visible spectrophotometer, FTIR, ¹HNMR, and GC-MS. ACEMB showed potent in vitro antioxidant property. Chronic administration of ACEMB prior to CCl₄ intoxication: i) attenuated the leakage of liver injury markers, such as, enzymes (AST, ALT, GGT, ALP and LDH) and biomolecules (bilirubin) into the blood circulation; ii) normalized the concentration of total proteins, albumin and globulin to control level; and iii) protected the liver against dyslipidemia. These effects of ACEMB show the preservation of endoplasmic reticulum function against CCl₄ toxicity in the liver. The protective effect of ACEMB was due to its antioxidant property, which was revealed by reduced oxidative stress (TBARS and HP) and enhanced functions of the endogenous antioxidative system (SOD, catalase, GPx, GST, GSH, vitamin E and C) against CCl₄ intoxication. Also, ACEMB protected the functional activities of the various mitochondrial tricarboxylic acid cycle and oxidative phosphorylation enzymes. The biochemical alterations are in concurrence with the histological observations, wherein ACEMB pretreatment prevented the vacuolation, degeneration of nuclei and necrosis of hepatocytes. In addition, in silico analysis reveals the interaction of ACEMB in the active site of cytochrome P450. ACEMB mediates hepatoprotective effect by substituting itself as an antioxidant and decreasing oxidative stress, thereby diminishing the intracellular organelle dysfunction against CCl₄ toxicity in the liver.