Design and synthesis of an oral prodrug alalevonadifloxacin for the treatment of MRSA infection.

Levonadifloxacin is a parenteral anti-MRSA benzoquinolizine antibacterial drug recently launched as, EMROK in India to treat acute bacterial skin and skin structure infections (ABSSSI) in hospitalized patients. As a step down therapy an oral form of levonadifloxacin with comparable PK/PD was needed because the levonadifloxacin exhibits very poor oral absorption. To improve the drugability in terms of oral absorption a pro-drug approach was evaluated. Structurally levonadifloxacin provides two sites amenable for ester or amide formation, a carboxyl function of benzoquinolizine pharmacophore and hydroxyl group on piperidine side chain. Several aliphatic, aromatic and amino acid esters of C-2 carboxylic acid, C-4-hydroxyl piperidine and double esters at both C-2, C-4 positions were synthesized. The cleavage of prodrugs was studied in vitro as well as in animal models to access their suitability as prodrug function. Among C-2 carboxylic ester prodrugs, daloxate (WCK 2320) showed highest cleavage in serum as well as in liver enzyme; however its stability in aqueous solution was unfavorable. In contrast, most of the esters at the hydroxyl group like propionyl ester (WCK 2305) and amino acid esters such as l-alanine (WCK 2349), l-valine (WCK 2630) were cleaved readily releasing active drug. Thus, indicating C-4-hydroxyl piperidine was amenable site for enzymatic cleavage over esters of C-2 carboxylic acid. Additionally, amino acid esters provided an opportunity to make salt, facilitating improved aqueous solubility. Methanesulfonate salt of l-alanine ester of levonadifloxacin (WCK 2349) was successfully developed and launched as oral prodrug alalevonadifloxacin (EMROK-O).

ROS-Responsive Selenium-Containing Carriers for Coencapsulation of Photosensitizer and Hypoxia-Activated Prodrug and Their Cellular Behaviors.

The integration of hypoxia-activated chemotherapy with photodynamic therapy (PDT) has newly become a potent strategy for tumor treatment. Herein, a reactive oxygen species (ROS)-responsive drug carriers (PS@AQ4N/mPEG-b-PSe NPs) are fabricated based on the amphiphilic selenium-containing methoxy poly(ethylene glycol)-polycarbonate (mPEG-b-PSe), the hydrophobic photosensitizer (PS), and hypoxia-activated prodrug Banoxantrone (AQ4N). The obtained nanoparticles are spherical with an average diameter of 100 nm as characterized by transmission electron microscope (TEM) and dynamic laser scattering (DLS) respectively. The encapsulation efficiency of the PS and AQ4N reaches 92.83% and 51.04% at different conditions, respectively, by UV-vis spectrophotometer. It is found that the drug release is accelerated due to the good ROS responsiveness of mPEG-b-PSe and the cumulative release of AQ4N is up to 89% within 30 h. The cell test demonstrates that the nanoparticles dissociate when triggered by the ROS stimuli in the cancer cells, thus the PS is exposed to more oxygen and the ROS generation efficiency is enhanced accordingly. The consumption of oxygen during PDT leads to the increased tumor hypoxia, and subsequently activates AQ4N into cytotoxic counterpart to inhibit tumor growth. Therefore, the synergistic therapeutic efficacy demonstrates this drug delivery has great potential for antitumor therapy.

Nucleotide analogues containing a pyrrolidine, piperidine or piperazine ring: Synthesis and evaluation of inhibition of plasmodial and human 6-oxopurine phosphoribosyltransferases and in vitro antimalarial activity.

Parasites of the Plasmodium genus are unable to produce purine nucleotides de novo and depend completely on the salvage pathway. This fact makes plasmodial hypoxanthine-guanine-(xanthine) phosphoribosyltransferase [HG(X)PRT] a valuable target for development of antimalarial agents. A series of nucleotide analogues was designed, synthesized and evaluated as potential inhibitors of Plasmodium falciparum HGXPRT, P. vivax HGPRT and human HGPRT. These novel nucleoside phosphonates have a pyrrolidine, piperidine or piperazine ring incorporated into the linker connecting the purine base to a phosphonate group(s) and exhibited a broad range of Ki values between 0.15 and 72 µM. The corresponding phosphoramidate prodrugs, able to cross cell membranes, have been synthesized and evaluated in a P. falciparum infected human erythrocyte assay. Of the eight prodrugs evaluated seven exhibited in vitro antimalarial activity with IC50 values within the range of 2.5-12.1 µM. The bis-phosphoramidate prodrug 13a with a mean (SD) IC50 of 2.5 ± 0.7 µM against the chloroquine-resistant P. falciparum W2 strain exhibited low cytotoxicity in the human hepatocellular liver carcinoma (HepG2) and normal human dermal fibroblasts (NHDF) cell lines at a concentration of 100 µM suggesting good selectivity for further structure-activity relationship investigations.

Design, synthesis, and evaluation of liver-specific gemcitabine prodrugs for potential treatment of hepatitis C virus infection and hepatocellular carcinoma.

Many successful anti-viral and anti-cancer drugs are nucleoside analogs, which disrupt RNA and/or DNA synthesis. Here, we present liver-specific prodrugs of the chemotherapy drug gemcitabine (2',2'-difluorodeoxycytidine) for the treatment of hepatitis C virus (HCV) infection and hepatocellular carcinoma. The prodrugs were synthesized by introducing aromatic functional moieties to the cytosine 4-NH2 group of gemcitabine via amide bonds. The chemical modification was designed to i) enable passive diffusion across cellular membrane, ii) protect the prodrugs from inactivating deamination by cellular enzymes, and iii) allow release of active gemcitabine after amide hydrolysis by high levels of carboxylesterases in the liver. We found that many of our prodrugs exhibited similar toxicity as gemcitabine toward liver- and kidney-derived cancer cell lines but were 24- to 620-fold less cytotoxic than gemcitabine in breast- and pancreas-derived cancer cells, respectively. The prodrugs also inhibited an HCV replicon with IC50 values ranging from 10 nM-1.7 µM. Moreover, many of the prodrugs had therapeutic index values of >10,000 and have synergetic effects when combined with other Food and Drug Administration-approved anti-HCV small molecule drugs. These characteristics support the development of gemcitabine prodrugs as liver-specific therapeutics.

Synthesis and Antiviral Activity of a Series of 2'-C-Methyl-4'-thionucleoside Monophosphate Prodrugs.

The NS5B RNA-dependent RNA polymerase of the hepatitis C virus (HCV) is a validated target for nucleoside antiviral drug therapy. We endeavored to synthesize and test a series of 4'-thionucleosides with a monophosphate prodrug moiety for their antiviral activity against HCV and other related viruses in the Flaviviridae family. Nucleoside analogs were prepared via the stereoselective Vorbrüggen glycosylation of various nucleobases with per-acetylated 2-C-methyl-4-thio-d-ribose built in a 10-step synthetic sequence from the corresponding ribonolactone. Conjugation of the thionucleoside to a ProTide phosphoramidate allowed for evaluation of the prodrugs in the cellular HCV replicon assay with anti-HCV activities ranging from single-digit micromolar (µM) to >200 µM. The diminished anti-HCV potency of our best compound compared to its 4'-oxo congener is the subject of ongoing research in our lab and is proposed to stem from changes in sugar geometry imparted by the larger sulfur atom.

Synthesis and biological evaluation of 5'-C-methyl nucleotide prodrugs for treating HCV infections.

Nucleotide prodrugs are of great clinical interest for treating a variety of viral infections due to their ability to target tissues selectively and to deliver relatively high concentrations of the active nucleotide metabolite intracellularly. However, their clinical successes have been limited, oftentimes due to unwanted in vivo metabolic processes that reduce the quantities of nucleoside triphosphate that reach the site of action. In an attempt to circumvent this, we designed novel nucleosides that incorporate a sterically bulky group at the 5'-carbon of the phosphoester prodrug, which we reasoned would reduce the amounts of non-productive PO bond cleavage back to the corresponding nucleoside by nucleotidases. Molecular docking studies with the NS5B HCV polymerase suggested that a nucleotide containing a 5'-methyl group could be accommodated. Therefore, we synthesized mono- and diphosphate prodrugs of 2',5'-C-dimethyluridine stereoselectively and evaluated their cytotoxicity and anti-HCV activity in the HCV replicon assay. All four prodrugs exhibited anti-HCV activity with IC50 values in the single digit micromolar concentrations, with the 5'(R)-C-methyl prodrug displaying superior potency relative to its 5'(S)-C-methyl counterpart. However, when compared to the unmethylated prodrug, the potency is poorer. The poorer potency of these prodrugs may be due to unfavorable steric interactions of the 5'-C-methyl group in the active sites of the kinases that catalyze the formation of active triphosphate metabolite.

Combination Therapy of Lung Cancer Using Layer-by-Layer Cisplatin Prodrug and Curcumin Co-Encapsulated Nanomedicine.

PURPOSE: Lung cancer remains the leading cancer-associated deaths worldwide. Cisplatin (CDDP) was used in combination with curcumin (CUR) for the treatment of non-small cell lung cancer. The aim of this study was to prepare and characterize CDDP prodrug and CUR co-encapsulated layer-by-layer nanoparticles (CDDP-PLGA/CUR LBL NPs) to induce cooperative response, maximize the therapeutic effect, overcome drug resistance, and reduce adverse side effects. METHODS: CDDP prodrug (CDDP-PLGA) was synthesized. CDDP-PLGA/CUR LBL NPs were constructed and their physicochemical properties were investigated by particle-size analysis, zeta potential measurement, drug loading, drug entrapment efficiency, and in vitro drug release behavior. In vitro cytotoxicity against human lung adenocarcinoma cell line (A549 cells) was investigated, and in vivo anti-tumor efficiency of CDDP-PLGA/CUR LBL NPs was evaluated on mice bearing A549 cell xenografts. RESULTS: CDDP-PLGA/CUR LBL NPs have a size of 179.6 ± 6.7 nm, a zeta potential value of -29.9 ± 3.2 mV, high drug entrapment efficiency of 85.6 ± 3.9% (CDDP) and 82.1 ± 2.8% (CUR). The drug release of LBL NPs exhibited a sustained behavior, which made it an ideal vehicle for drug delivery. Furthermore, CDDP-PLGA/CUR LBL NPs could significantly enhance in vitro cytotoxicity and in vivo antitumor effect against A549 cells and lung cancer animal model compared to the single drug-loaded LBL NPs and free drug groups. CONCLUSION: CDDP-PLGA/CUR LBL NPs were reported for the first time in the combination therapy of lung cancer. The results demonstrated that the CDDP-PLGA/CUR LBL NPs might be a novel promising system for the synergetic treatment of lung carcinoma.

Identification of Parthenolide Dimers as Activators of Pyruvate Kinase M2 in Xenografts of Glioblastoma Multiforme in Vivo.

Herein we detail the discovery of a series of parthenolide dimers as activators of PKM2 and evaluation of their anti-GBM activities. The most promising compound 5 showed high potency to activate PKM2 with an AC50 value of 15 nM, inhibited proliferation and metastasis, and induced apoptosis of GBM cells. Compound 5 could promote tetramer formation of PKM2 and reduce nucleus translocation of PKM2 in GBM cells without influence on the expression of total PKM2, thereby inhibiting the STAT3 signal pathway in vitro and in vivo. PKM2 knockdown assay demonstrated that the anti-GBM effect of 5 mainly depended on the expression of PKM2 in vitro and in vivo. Compound 16, a prodrug of 5, markedly suppressed U118 tumor xenograft growth and reduced the weight of tumor. On the basis of these investigations, we propose that 16 might be considered as a promising lead compound for discovery of anti-GBM drugs.

Pharmacological and biotransformation studies of 1-acyl-substituted derivatives of d-lysergic acid diethylamide (LSD).

The ergoline d-lysergic acid diethylamide (LSD) is one of the most potent psychedelic drugs. 1-Acetyl-LSD (ALD-52), a derivative of LSD containing an acetyl group on the indole nitrogen, also produces psychedelic effects in humans and has about the same potency as LSD. Recently, several other 1-acyl-substitued LSD derivatives, including 1-propanoyl-LSD (1P-LSD) and 1-butanoyl-LSD (1B-LSD), have appeared as designer drugs. Although these compounds are assumed to act as prodrugs for LSD, studies have not specifically tested this prediction. The present investigation was conducted to address the gap of information about the pharmacological effects and mechanism-of-action of 1-acyl-substituted LSD derivatives. Competitive binding studies and calcium mobilization assays were performed to assess the interaction of ALD-52, 1P-LSD, and 1B-LSD with serotonin 5-HT2 receptor subtypes. A receptorome screening was performed with 1B-LSD to assess its binding to other potential targets. Head twitch response (HTR) studies were performed in C57BL/6J mice to assess in vivo activation of 5-HT2A (the receptor thought to be primarily responsible for hallucinogenesis). Finally, liquid chromatography/ion-trap mass spectrometry (LC/MS) was used to quantify plasma levels of LSD in Sprague-Dawley rats treated with ALD-52 and 1P-LSD. 1-Acyl-substitution reduced the affinity of LSD for most monoamine receptors, including 5-HT2A sites, by one to two orders of magnitude. Although LSD acts as an agonist at 5-HT2 subtypes, ALD-52, 1P-LSD and 1B-LSD have weak efficacy or act as antagonists in Ca2+-mobilization assays. Despite the detrimental effect of 1-acyl substitution on 5-HT2A affinity and efficacy, 1-acyl-substitued LSD derivatives induce head twitches in mice with relatively high potency. High levels of LSD were detected in the plasma of rats after subcutaneous administration of ALD-52 and 1P-LSD, demonstrating these compounds are rapidly and efficiently deacylated in vivo. These findings are consistent with the prediction that ALD-52, 1P-LSD and 1B-LSD serve as prodrugs for LSD. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Bifunctional supramolecular prodrug vesicles constructed from a camptothecin derivative with a water-soluble pillar[5]arene for cancer diagnosis and therapy.

Bifunctional supramolecular prodrug vesicles have been successfully constructed based on the complexation between a glutathione (GSH)-responsive prodrug guest molecule (DNS-CPT) and a water-soluble pillar[5]arene (WP5) for cancer diagnosis and therapy. Under the microenvironment of cancer cells with high GSH concentration, 7-ethyl-10-hydroxycamptothecin (SN-38) with strong yellow fluorescence can be efficiently released from the prodrug DNS-CPT for drug location and cancer therapy.

An easy access to topical gels of an anti-cancer prodrug (5-fluorouracil acetic acid) for self-drug-delivery applications.

An easy access to topical gels (both hydro- and organogels) derived from an anti-cancer prodrug namely 5-fluorouracil acetic acid (5-FuA) achieved by exploiting a simple salt formation strategy is reported for the first time. Nearly 85% of the salts synthesized were gelators. Single crystal structures of some of the gelator salts revealed an intriguing hydrogen bonding network including double stranded 1D chains stabilized through uracil-uracil complementary interactions and the crystal structures of the gelator salts corroborated well with the hypothesis based on which the gelators were designed. Studies indicated that both the hydrogel and the methyl salicylate gel of the gelator salt FuA-15 were suitable for self-drug-delivery application.

Lung cancer therapy using doxorubicin and curcumin combination: Targeted prodrug based, pH sensitive nanomedicine.

Lung cancer is the leading cause of cancer death worldwide. To overcome the toxic side effects and multidrug resistance (MDR) during doxorubicin (DOX) chemotherapy, a urokinase plasminogen activator receptor (uPAR) targeting U11 peptide decorated, pH-sensitive, dual drugs co-encapsulated nanoparticles (NPs) system is employed in this study. A U11 peptide conjugated, pH-sensitive DOX prodrug (U11-DOX) was synthesized and used as materials to produce NPs. A curcumin (CUR) and U11-DOX co-encapsulated NPs system (U11-DOX/CUR NPs) was constructed to treat lung cancer. After the characterization of biophysical properties of this NPs system, synergistic chemotherapeutic efficacy was evaluated in both cultured cancer cells and tumor-bearing animal model. U11-DOX/CUR NPs had a uniformly spherical shape with a core-shell structure. The mean particle size and zeta potential of the U11-DOX/CUR NPs was 121.3 nm and -33.5 mV, with a DOX and CUR EE of 81.7 and 90.5%, respectively. The DOX release from U11-DOX/CUR NPs was 83.5, 55.2, and 32.8% correspondence to the pH of 5.0, 6.0 and 7.4. Cellular uptake efficiency of U11-DOX/CUR NPs was significantly higher than non U11 peptide decorated DOX/CUR NPs. U11-DOX/CUR NPs displayed a pronounced synergy effects in vitro and an obvious tumor tissue accumulation efficiency in vivo. In vivo antitumor experiment showed that U11-DOX/CUR NPs could inhibit the tumor growth to a level of 85%.In vitro and in vivo studies demonstrated that U11-DOX/CUR NPs is a sustained released, pH responsive, synergistic antitumor system. This study suggests that the U11-DOX/CUR NPs have promising potential for combination treatment of lung cancer.

Prodrugs for colon-restricted delivery: Design, synthesis, and in vivo evaluation of colony stimulating factor 1 receptor (CSF1R) inhibitors.

The ability to restrict low molecular weight compounds to the gastrointestinal (GI) tract may enable an enhanced therapeutic index for molecular targets known to be associated with systemic toxicity. Using a triazolopyrazine CSF1R inhibitor scaffold, a broad range of prodrugs were synthesized and evaluated for enhanced delivery to the colon in mice. Subsequently, the preferred cyclodextrin prodrug moiety was appended to a number of CSF1R inhibitory active parent molecules, enabling GI-restricted delivery. Evaluation of a cyclodextrin prodrug in a dextran sodium sulfate (DSS)-induced mouse colitis model resulted in enhanced GI tissue levels of active parent. At a dose where no significant depletion of systemic monocytes were detected, the degree of pharmacodynamic effect-measured as reduction in macrophages in the colon-was inferior to that observed with a systemically available positive control. This suggests that a suitable therapeutic index cannot be achieved with CSF1R inhibition by using GI-restricted delivery in mice. However, these efforts provide a comprehensive frame-work in which to pursue additional gut-restricted delivery strategies for future GI targets.

New series of 3,5-disubstituted tetrahydro-2H-1,3,5-thiadiazine thione (THTT) derivatives: Synthesis and potent antileishmanial activity.

Four series of heterocyclic compounds, namely, tetrahydro-2H-1,3,5-thiadiazine thione derivatives were synthesized in good to excellent yields and were screened for their in vitro antileishmanial activities against Leishmania major (promastigotes). Most of the compounds showed significant antileishmanial activity within the range of IC50 = 15.48-39.36 µM when compared with standard pentamidine (IC50 = 14.95 µM). The structure-activity relationship showed that N-3 and N-5 substituents have a key role against leishmanicidal activity. The ester analogues (series B) were found to have a 1.5 to 5-fold reduced activity compared to their acidic counterparts. Cytotoxicity against mammalian mouse fibroblast 3 T3 cells was also evaluated and compared between the acid and its ester analogue. The reduction of antileishmanial activity and loss of toxicity in the newly developed THTT ester derivative indicates that these compounds can be used as a template study for the production of effective antileishmanial ester prodrugs.

Novel Antihypertensive Prodrug from Grape Seed Proanthocyanidin Extract via Acid-Mediated Depolymerization in the Presence of Captopril: Synthesis, Process Optimization, and Metabolism in Rats.

Grape seed extract contains a high content of proanthocyanidins that can be depolymerized into C-4-substituted (epi)catechin derivatives in the presence of nucleophiles. However, the biological and medicinal values of depolymerization products have been rarely investigated. Recently, we developed a novel depolymerization product (-)-epicatechin-4ß- S-captopril methyl ester (ECC) derived from the reaction of grape seed proanthocyanidin extract with captopril in the presence of acidified methanol. A central composite design was employed to select the most appropriate depolymerization temperature and time to obtain the target product ECC with a high yield. A total of 16 metabolites of ECC in rat urine, feces, and plasma were identified using liquid chromatography quadrupole time-of-flight tandem mass spectrometry. The in vivo results suggested that ECC could release captopril methyl ester and epicatechin, followed by the generation of further metabolites captopril and epicatechin sulfate conjugates. Therefore, ECC may be used as a potential prodrug with synergistic or additive hypotensive effects.

Phenolic acid-tethered isoniazid for abrogation of drug-induced hepatotoxicity: design, synthesis, kinetics and pharmacological evaluation.

Morphological and metabolic aberrations in the liver caused by long-term use of anti-tubercular agent isoniazid (INH) have been an issue of great concern in tuberculosis treatment. To resolve this issue, a novel hepatoprotective prodrug strategy was developed by combining the antioxidant property of phenolic acids with INH moiety for probable synergistic effect. In this work, INH was conjugated with phenolic antioxidants using Schotten-Baumann reaction through biocleavable amide linkage. Synthesized prodrugs were characterized by spectral analysis and in vitro release studies were carried out using HPLC. They were found to be stable in acidic (pH 1.2), basic (pH 7.4) buffers, stomach homogenates of rat whereas hydrolyzed significantly (56.03-88.62%) in intestinal homogenates over a period of 6 h. Further their hepatoprotective potential was evaluated in male Wistar rats by performing liver function tests, oxidative stress markers, and histopathology studies. All the prodrugs were effective in abating oxidative stress and re-establishing normal hepatic physiology. Especially the effect of prodrugs of INH with gallic acid and syringic acid in restoring levels of enzymes superoxide dismutase and glutathione peroxidase and abrogating liver damage was noteworthy. The findings of this investigation demonstrated that reported prodrugs can add safety and efficacy to future clinical protocols of tuberculosis treatment.

Dual-targeting for brain-specific drug delivery: synthesis and biological evaluation.

Ibuprofen is one of the most potent non-steroid anti-inflammatory drugs (NSAIDs) and plays an important role in the treatment of neurodegenerative diseases. However, its poor brain penetration and serious side effects at therapeutic doses, has hindered its further application. Thus, it is of great interest to develop a carrier-mediated transporter (CMT) system that is capable of more efficiently delivering ibuprofen into the brain at smaller doses to treat neurodegenerative diseases. In this study, a dual-mediated ibuprofen prodrug modified by glucose (Glu) and vitamin C (Vc) for central nervous system (CNS) drug delivery was designed and synthesized in order to effectively deliver ibuprofen to brain. Ibuprofen could be released from the prepared prodrugs when incubated with various buffers, mice plasma and brain homogenate. Also, the prodrug showed superior neuroprotective effect in vitro and in vivo than ibuprofen. Our results suggest that chemical modification of therapeutics with warheads of glucose and Vc represents a promising and efficient strategy for the development of brain-targeting prodrugs by utilizing the endogenous transportation mechanism of the warheads.

Environmentally Triggerable Retinoic Acid-Inducible Gene I Agonists Using Synthetic Polymer Overhangs.

Retinoic acid-inducible gene I (RIG-I) is a cytosolic pattern recognition receptor (PRR) that potently activates antiviral innate immunity upon recognition of 5' triphosphorylated double-stranded RNA (pppRNA). Accordingly, RNA ligands of the RIG-I pathway have recently emerged as promising antiviral agents, vaccine adjuvants, and cancer immunotherapeutics. However, RIG-I is expressed constitutively in virtually all cell types, and therefore administration of RIG-I agonists causes risk for systemic inflammation and possible dose-limiting toxicities. Here, we establish proof-of-concept and initial design criteria for pppRNA prodrugs capable of activating the RIG-I pathway in response to specific environmental stimuli. We show that covalent conjugation of poly(ethylene glycol) (PEG) to the 3' end of the complementary strand, i.e., on the same side but opposite strand as the 5' triphosphate group, can generate a synthetic overhang that prevents RIG-I activation. Additionally, conjugation of PEG through a cleavable linker-here, a reducible disulfide bond-allows for removal of the synthetic overhang and restoration of immunostimulatory activity. Furthermore, we demonstrate that blockade of RIG-I activation via synthetic overhangs is dependent on PEG molecular weight, with a critical molecular weight between 550 and 1000 Da required to inhibit activity. Additionally, we demonstrate that blockade of RIG-I activity is conjugation site-dependent, as ligation of PEG to the opposite end of the RNA did not influence ligand activity. Collectively, this work demonstrates that conjugation of synthetic polymer overhangs to pppRNA through cleavable linkers is a viable strategy for the development of environmentally triggerable RIG-I-targeting prodrugs.

Synthesis and biological evaluation of a novel ß-D-2'-deoxy-2'-α-fluoro-2'-ß-C-(fluoromethyl)uridine phosphoramidate prodrug for the treatment of hepatitis C virus infection.

A novel ß-D-2'-deoxy-2'-α-fluoro-2'-ß-C-(fluoromethyl)uridine phosphoramidate prodrug (1) has been synthesized. This compound exhibits submicromolar-level antiviral activity in vitro against HCV genotypes 1b, 1a, 2a, and S282T replicons (EC50 = 0.18-1.13 µM) with low cytotoxicity (CC50 > 1000 µM). Administered orally, prodrug 1 is well tolerated at doses of up to 4 g/kg in mice, and produces a high level of the corresponding triphosphate in rat liver.

Amino acid and peptide prodrugs of diphenylpropanones positive allosteric modulators of α7 nicotinic receptors with analgesic activity.

α7 Nicotinic acetylcholine receptors (nAChRs) are ion channels implicated in a number of CNS pathological processes, including pain and psychiatric, cognitive and inflammatory diseases. Comparing with orthosteric agonism, positive allosteric modulation of these channels constitutes an interesting approach to achieve selectivity versus other nicotinic receptors. We have recently described new chalcones and 1,3-diphenylpropanones as positive allosteric modulators (PAMs) of α7 nAChRs, which proved to have good analgesic activities but poor pharmacokinetic properties. Here we report the preparation of amino acid and peptide derivatives as prodrugs of these modulators with the aim of improving their in vivo biological activity. While the valine derivative showed very short half life in aqueous solutions to be considered a prodrug, Val-Val and Val-Pro-Val are suitable precursors of the parent 1,3-diphenylpropanones, via chemical and enzymatic transformation, respectively. Compounds 19 (Val-Val) and 21 (Val-Pro-Val), prodrugs of the 2',5',4-trihydroxy-1,3-diphenylpropan-1-one 3, showed significant antinociceptive activity in in vivo assays. The best compound, 21, displayed a better profile in the analgesia test than its parent compound 3, exhibiting about the same potency but long-lasting effects.