Cyclic amide derivatives as potential prodrugs II: N-hydroxymethylsuccinimide- / isatin esters of some NSAIDs as prodrugs with an improved therapeutic index

Drug/Lead Compound Hydroxymethylation as a Simple Approach to Enhance Pharmacodynamic and Pharmacokinetic Properties

Hydroxymethylation is a simple chemical reaction, in which the introduction of the hydroxymethyl group can lead to physical–chemical property changes and offer several therapeutic advantages, contributing to the improved biological activity of drugs. There are many examples in the literature of the pharmaceutical, pharmacokinetic, and pharmacodynamic benefits, which the hydroxymethyl group can confer to drugs, prodrugs, drug metabolites, and other therapeutic compounds. It is worth noting that this group can enhance the drug’s interaction with the active site, and it can be employed as an intermediary in synthesizing other therapeutic agents. In addition, the hydroxymethyl derivative can result in more active compounds than the parent drug as well as increase the water solubility of poorly soluble drugs. Taking this into consideration, this review aims to discuss different applications of hydroxymethyl derived from biological agents and its influence on the pharmacological effects of drugs, prodrugs, active metabolites, and compounds of natural origin. Finally, we report a successful compound synthesized by our research group and used for the treatment of neglected diseases, which is created from the hydroxymethylation of its parent drug.

Amide-Type Substrates in the Synthesis of N-Protected 1-Aminomethylphosphonium Salts

Herein we describe the development and optimization of a two-step procedure for the synthesis of N-protected 1-aminomethylphosphonium salts from imides, amides, carbamates, or lactams. Our “step-by-step” methodology involves the transformation of amide-type substrates to the corresponding hydroxymethyl derivatives, followed by the substitution of the hydroxyl group with a phosphonium moiety. The first step of the described synthesis was conducted based on well-known protocols for hydroxymethylation with formaldehyde or paraformaldehyde. In turn, the second (substitution) stage required optimization studies. In general, reactions of amide, carbamate, and lactam derivatives occurred at a temperature of 70 °C in a relatively short time (1 h). On the other hand, N-hydroxymethylimides reacted with triarylphosphonium salts at a much higher temperature (135 °C) and over longer reaction times (as much as 30 h). However, the proposed strategy is very efficient, especially when NaBr is used as a catalyst. Moreover, a simple work-up procedure involving only crystallization afforded good to excellent yields (up to 99%).

Synthesis and biological evaluation of new nicotinate derivatives as potential anti-inflammatory agents targeting COX-2 enzyme

Two novel series derived from nicotinic acid were synthesized and evaluated for their inhibitory activity against cyclooxygenases COX-1 and COX-2, and their selectivity indices were determined. Celecoxib, diclofenac and indomethacin were used as reference drugs. All compounds showed highly potent COX-2 inhibitory activity and higher selectivity towards COX-2 inhibition compared to indomethacin. In addition, these compounds except 3a showed clear preferential COX-2 over COX-1 inhibition compared to diclofenac. Compounds 3b, 3e, 4c and 4f showed COX-2 inhibitory activity equipotent to celecoxib. Compounds 4c and 4f demonstrated selectivity indices 1.8-1.9 fold higher than celecoxib. These two most potent and COX-2 selective compounds were further tested in vivo for anti-inflammatory activity by means of carrageenan induced rat paw edema method. Ulcerogenic activity with histopathological studies were performed. The results showed no ulceration, which implies their safe gastric profile. Compound 4f exhibited the most potent in vivo anti-inflammatory activity comparable to all reference drugs. Further, compounds 4c and 4f were investigated for their influence on certain inflammatory cytokines TNF-α and IL-1β in addition to PEG2. The findings revealed that these candidates could be identified as promising potent anti-inflammatory agents. Molecular docking of 4c and 4f in the COX-2 active site was performed to rationalize their COX-2 inhibitory potency. The results were found to be in line with the biological findings as they exerted more favorable interactions compared to that of celecoxib, explaining their remarkable COX-2 inhibitory activity.

Synthesis, comparative docking, and pharmacological activity of naproxen amino acid derivatives as possible anti-inflammatory and analgesic agents

Background and aim: Naproxen is a member of the Nonsteroidal anti-inflammatory drugs (NSAIDs). This work aimed to synthesize a safe NSAID agent based on a peptide derivative.

Methods: The structure of compounds 5–20 was established on the basis of spectral data. Frontier molecular orbitals and chemical reactivity were discussed to clarify inter- and intramolecular interactions among tested compounds. We applied competitive molecular docking using polynomial logarithms to identify the most accurate algorithm for pharmacological activity prediction for the tested compounds. The docking protocol with the lowest RMSD was selected for analyzing binding affinity.

Results: Docking results illustrated that the binding interaction increased after introduction of an acidic fragment to the parent compound. These compounds were selected for additional study against adsorption, distribution, metabolism, excretion, and toxicity (ADMET) in silico. The compounds tested had good oral bioavailability without any carcinogenesis effect; no marked health effects were observed via rodent toxicity. Compounds passed through docking and ADMET profiles for them (5–16) were examined as anti-inflammatory and analgesic agents. Compounds 8 and 16 showed higher anti-inflammatory potency than the reference drug and tested compounds. Compounds 8, 10, and 14 exhibited the highest analgesic potency compared to the other tested compounds.

Conclusion: The tested compounds have shown negligible ulcerogenic effects, and may be considered safer drugs than naproxen for treating inflammatory conditions.

Synthesis and evaluation of novel mutual prodrugs of Piroxicam

Therapeutic efficacy of piroxicam can be improved by retarding gastrointestinal side effects by means of temporarily modification of enolic hydroxyl group chemically. The NSAIDs such as aceclofenac, ibuprofen, mefenamic acid and naproxen were selected as promoities with the aim of getting synergistic effect through these well known pharmaco-counter parts. The targeted prodrugs are synthesized successfully and confirmed by characterization. Synthesis involved chlorination of NSAIDs and coupling of this acid chloride with piroxicam through enolic hydroxyl group to get ester derivatives. Mutual prodrugs were evaluated by hydrolysis study at different pH (acidic, neutral, alkaline) using phosphate buffer. Prodrug derivatives were found to be stable at acidic and neutral pH but prone to hydrolysis at alkaline pH. Thus the objective of the presented study was to overcome the undesirable side effects of NSAIDs. Thus, current studies confirms that the mutual prodrug approach can be applied  effectively in order to  achieve the purpose of raising effectiveness of piroxicam under two lines; firstly, masking of enolic hydroxyl group through acids and converting them to esters and secondly, utilizing the known NSAIDs for achieving the synergistic effect.

Synthesis, characterization and pharmacological evaluation of certain enzymatically cleavable NSAIDs amide prodrugs

The presence of free carboxylic acid group in majority of non-steroidal anti-inflammatory drug (NSAIDs) is responsible from GI irritation. Coupling of the appropriate NSAIDs (diclofenac, naproxen, dexibuprofen and meclofenamic acid) 1-4, respectively with the appropriate amino acid ester 5 using dicyclohexylcarbodiimide afforded prodrugs 6-13. The structures of the prodrugs were verified based on spectral data. Chemical hydrolysis studies performed in three different non enzymatic buffer solutions at pH 1.2, 5.5 and 7.4, as well as in 80% human plasma and 10% rat liver homogenate using HPLC indicate no conversion of prodrugs to their respective NSAID in the studied buffers, while they underwent a reasonable plasma and rat liver homogenate hydrolysis. Furthermore, ulcerogenicity of prodrugs 9 and 12 were studied and results revealed no gastro-ulcerogenic effects.

Flurbiprofen-antioxidant mutual prodrugs as safer nonsteroidal anti-inflammatory drugs: synthesis, pharmacological investigation, and computational molecular modeling

Flurbiprofen-antioxidant mutual prodrugs were synthesized to reduce the gastrointestinal (GI) effects associated with flurbiprofen. For reducing the GI toxicity, the free carboxylic group (-COOH) was temporarily masked by esterification with phenolic -OH of natural antioxidants vanillin, thymol, umbelliferone, and sesamol. The in vitro hydrolysis of synthesized prodrugs showed that they were stable in buffer solution at pH 1.2, indicating their stability in the stomach. The synthesized prodrugs undergo significant hydrolysis in 80% human plasma and thus release free flurbiprofen. The minimum reversion was observed at pH 1.2, suggesting that prodrugs are less irritating to the stomach than flurbiprofen. The anti-inflammatory, analgesic, antipyretic, and ulcerogenic activities of prodrugs were evaluated. All the synthesized prodrugs significantly (P<0.001) reduced the inflammation against carrageenan and egg albumin-induced paw edema at 4 hours of study. The reduction in the size of the inflamed paw showed that most of the compounds inhibited the later phase of inflammation. The prodrug 2-oxo-2H-chromen-7-yl-2-(2-fluorobiphenyl-4-yl)propanoate (4b) showed significant reduction in paw licking with percentage inhibition of 58%. It also exhibited higher analgesic activity, reducing the number of writhes with a percentage of 75%, whereas flurbiprofen showed 69% inhibition. Antipyretic activity was investigated using brewer's yeast-induced pyrexia model, and significant (P<0.001) reduction in rectal temperature was shown by all prodrugs at all times of assessment. The results of ulcerogenic activity showed that all prodrugs produced less GI irritation than flurbiprofen. Molecular docking and simulation studies were carried out with cyclooxygenase (COX-1 and COX-2) proteins, and it was observed that our prodrugs have more potential to selectively bind to COX-2 than to COX-1. It is concluded that the synthesized prodrugs have promising pharmacological activities with reduced GI adverse effects than the parent drug.

A novel NSAID derivative, phospho-ibuprofen, prevents AOM-induced colon cancer in rats

The cancer chemopreventive properties and gastrointestinal toxicity of ibuprofen are well documented. Modification of existing NSAIDs has improved on the chemopreventive efficacy of this agent and reduced its toxicity. In this study, ibuprofen and a modified derivative (phospho-modified ibuprofen or p-ibuprofen) were used in a chemically induced model of colon cancer. Fisher 344 rats were injected with azoxymethane then treated with either ibuprofen (500 ppm) or p-ibuprofen (900 ppm) for 20 weeks to observe aberrant crypt foci (ACF) or 40 weeks to evaluate tumor incidence and multiplicity. β-catenin and p65 were measured in colonic tissues by immunofluorescence staining. Equal molar doses of ibuprofen (75 and 670 mg/kg) and p-ibuprofen (135 and 1,215 mg/kg) were administered to rats for 7 days to assess acute toxicity. The in vitro effect of p-ibuprofen on COX-2 and PGE(2) synthesis, β-catenin expression and NF-κB activity were examined in RAW 264.7 macrophage and HCT 116 colon cancer cells. At week 20, p-ibuprofen and ibuprofen significantly reduced the multiplicity of ACF compared with control (p<0.05); 31.2 and 37.9%, respectively. At week 40, p-ibuprofen and ibuprofen reduced the multiplicity of colon tumors compared with control (p<0.01) by 47.2 and 56.6%, respectively. Equal molar concentrations of ibuprofen (670 mg/kg) and p-ibuprofen (1,215 mg/kg) resulted in stomach ulceration in 85.7% (6 out of 7) and 14.3% (1 out of 7) of rats, respectively, with p<0.01. Immunofluoresence staining and western blot analysis demonstrated that both ibuprofen and p-ibuprofen suppressed β-catenin nuclear translocation in colon cancer cells. In addition, p-ibuprofen but not ibuprofen inhibited NF-κB activation in colon cancer cells. Collectively, these results suggest that p-ibuprofen is a potential effective novel drug for long-term use in colon cancer prevention.

Single oral dose study of two isosorbide-based aspirin prodrugs in the dog

The objective of this study was to compare two aspirin prodrugs, isosorbide diaspirinate (ISDA) and a nitroaspirin (ISMNA), with aspirin in terms of effects on dog platelet function after administration of a single oral dose. Groups of six dogs were administered ISDA (2 mg kg−1), ISMNA (4 mg kg−1) or aspirin (2 mg kg−1). Blood was sampled at 1, 2, 4, 8, 12 and 24 h post-dosing and evaluated for capacity to generate post-clotting thromboxane (TX)B2. The aggregation response to arachidonic acid (AA) (100 μM), ADP (30 μM) or collagen (10 μg mL−1) was estimated at each time-point using the whole blood impedance method. Plasma ISMN following oral administration of ISMNA was also measured and compared with plasma ISMN following administration of a physical mixture of ISMN and aspirin. ISDA administration (2 mg kg−1) was associated with a significant reduction (P&lt; 0.05) in serum TXB2 at 12 and 24 h (&gt;90%) post-dosing and persistent inhibition of AA-induced platelet aggregation. ISDA administration caused a more marked depression of post-clotting TXB2 levels than aspirin in this study, although its ability to inhibit platelet aggregation was less consistent than that of aspirin. The nitroaspirin ISMNA was least effective at inhibiting platelet aggregation response or TXB2 production. The ISMN AUC0–24h for the ISMNA-treated dogs was 77% of that for the physical mix-treated dogs and the tmax was delayed. This study indicates that the two aspirin esters cause aspirin-like effects on platelet function, probably through aspirin release, when administered orally to dogs.

Study of Ibuprofen Glucopyranoside Derivative Synthesis byCandida antarcticaLipase in Organic Solvent

The direct esterification of ibuprofen and methyl alpha-D-glucopyranoside in organic solvent by Novozym 435 was investigated in terms of the main variables controlling the process, including initial water activity (a(w), 0.05-0.75), incubation time, (0-168 h) and substrate concentration. The results showed that the lower initial aw values resulted in higher enzymatic activity and bioconversion yield. The most appropriate initial aw and incubation time were 0.06 and 144 h, respectively. The results also showed that the optimal ratio of ibuprofen to methyl alpha-D-glucopyranoside was 2.0. By optimizing these parameters, the yield increased about 50%. In addition, the product was confirmed to be methyl 6-O-(2'-(4'-isobutylphenyl) propionyl) D-alpha-glucopyranoside.

Synthesis and properties of a naproxen polymeric prodrug

A water-soluble polymeric prodrug containing a naproxen moiety was synthesized. The carboxylic groups of naproxen were condensed with the hydroxyl groups of 2-hydroxyethyl methacrylate (HEMA) to produce a drug-linked monomer, denoted HN. The polymeric prodrug was prepared by copolymerization of HN with methacrylic acid. The molar percentage of HN in the polymeric prodrug was 26 mol%, as determined by 1H NMR. To investigate the pertinence of this polymeric prodrug, the hydrolysis was studied in-vitro with or without esterase or lipase. The kinetics of enzymatic catalysis was calculated from a Lineweaver-Burk plot. The anti-inflammatory activity was evaluated using the carrageenan-induced oedema test. The polymeric prodrug released a major fraction of the free naproxen and a significant fraction of the hydroxyethyl ester derived-naproxen. The maximum hydrolysis rate Vmax, and the Michaelis constant Km were calculated to be 2.16 x 10(-5) equiv. mol L-1 min-1 and 5.11 x 10(-2) equiv. mol L-1. The maximum anti-inflammatory inhibition of free naproxen appeared at 2 h and quickly decreased thereafter. In contrast, the polymeric prodrug showed a maximum at around 2-3 h and then slowly decreased. This indicates that the polymeric prodrug displays greater potency than free naproxen in the inhibition of acute inflammatory processes over long periods.