Synthesis and hydrolytic behavior of two novel tripartate codrugs of naltrexone and 6beta-naltrexol with hydroxybupropion as potential alcohol abuse and smoking cessation agents

Mechanochemistry Frees Thiourea Dioxide (TDO) from the 'Veils' of Solvent, Exposing All Its Reactivity

The synthesis of nitrogen-based heterocycles has always been considered essential in developing pharmaceuticals in medicine and agriculture. This explains why various synthetic approaches have been proposed in recent decades. However performing as methods, they often imply harsh conditions or the employment of toxic solvents and dangerous reagents. Mechanochemistry is undoubtedly one of the most promising technologies currently used for reducing any possible environmental impact, addressing the worldwide interest in counteracting environmental pollution. Following this line, we propose a new mechanochemical protocol for synthesizing various heterocyclic classes by exploiting thiourea dioxide (TDO)'s reducing proprieties and electrophilic nature. Simultaneously exploiting the low cost of a component of the textile industry such as TDO and all the advantages brought by a green technique such as mechanochemistry, we plot a route towards a more sustainable and eco-friendly methodology for preparing heterocyclic moieties.

PIFA-Mediated Tandem Hofmann-Type Rearrangement and Cyclization Reaction of α-Acyl-β-aminoacrylamides: Access to Polysubstituted Oxazol-2(3H)-ones

An efficient and straightforward synthesis of polysubstituted oxazol-2(3H)-ones has been developed via a tandem Hofmann-type rearrangement and cyclization reaction of various α-acyl-β-aminoacrylamides mediated by phenyl iodine(III) bis(trifluoroacetate) (PIFA) in the presence of trifloroacetic acid (TFA). This novel protocol features readily available starting materials, mild reaction conditions, simple execution, high chemoselectivity, good functional group tolerance, and a metal-free oxidation process.

PIFA-BF3·OEt2 mediated intramolecular regioselective domino cyclization of ynamides: A novel method for the synthesis of tetrahydroisoquinoline-oxazol-2(3H)-ones

The transition metal-free intramolecular regioselective domino cyclization of N-Boc protected ynamides has been developed to provide the corresponding tetrahydroisoquinoline-oxazo-2(3H)-ones in moderate to good yields.

Pd/Cu-Catalyzed tandem head-to-tail dimerization/cycloisomerization of terminal ynamides for the synthesis of 5-vinyloxazolones

This is the first Pd/Cu-catalyzed tandem head-to-tail dimerization/cycloisomerization of terminal ynamides for the synthesis of 5-vinyl-oxazolones.

Bupropion Hydrochloride

Bupropion hydrochloride is a norepinephrine-dopamine disinhibitor (NDDI) approved for the treatment of depression and smoking cessation. Bupropion is a trimethylated monocyclic phenylaminoketone second-generation antidepressant, which differs structurally from most antidepressants, and resides in a novel mechanistic class that has no direct action on the serotonin system. Comprehensive chemical, physical, and spectroscopic profiles are presented. This analytical profile provides an extensive spectroscopic investigation utilizing mass spectrometry, one- and two-dimensional NMR, solid-state NMR, IR, NIR, Raman, UV, and X-ray diffraction. The profile also includes significant wet chemistry studies for pH, solubility, solution, and plasma stability. Both HPLC and UPLC methodology are presented for bupropion and its related impurities or major metabolites. The profile concludes with an overview of biological properties that includes toxicity, drug metabolism, and pharmacokinetics.

Synthesis and in vitro stability of amino acid prodrugs of 6-β-naltrexol for microneedle-enhanced transdermal delivery

A small library of amino acid ester prodrugs of 6-β-naltrexol (NTXOL, 1) was prepared in order to investigate the candidacy of these prodrugs for microneedle-enhanced transdermal delivery. Six amino acid ester prodrugs were synthesized (6a-f). 6b, 6d, and 6 e were stable enough at skin pH (pH 5.0) to move forward to studies in 50% human plasma. The lead compound (6 e) exhibited the most rapid bioconversion to NTXOL in human plasma (t1/2 = 2.2 ± 0.1h).

Synthesis, screening and pharmacokinetic evaluation of potential prodrugs of bupropion. Part one: in vitro development

In general, prodrugs are developed to circumvent deficiencies associated with the absorption, distribution, metabolism, excretion or toxicological (ADMET) profile associated with the active drug. In our study, we select bupropion, a drug with broad pharmacology incorporating dopaminergic, noradrenergic, nicotinic and cytokine modulation properties, but which is rapidly metabolized in vivo. We exploited its carbonyl and secondary amine functionality to facilitate the synthesis of bioprecursor prodrug forms with the sole objective of identifying analogues with enhanced properties over bupropion. A range of analogues were synthesized, ranging from N-methyl, N-benzyl, oximes, enol acetate and ether forms to examples where both functional groups were utilized to form oxadiazine, oxadiazinone, oxazolone and acetylated derivatives. We then developed an in vitro metabolic screen to simulate the human oral delivery route for these analogues. The selection of media in the screens contained a variety of pH, enzymatic and co-factor systems which mimic metabolic in vivo environments that drugs encounter when delivered orally. By coupling our in vitro screening tool to a selective hyphenated technique such as LC-MS, we were able to quickly select potential prodrugs for further in vitro and in vivo development. From the data generated, the N-alkylated bupropion analogues were shown to have the highest potential to act as bioprecursor prodrugs of bupropion.

Microneedle-assisted percutaneous delivery of naltrexone hydrochloride in yucatan minipig: in vitro-in vivo correlation

Although microneedle-assisted transdermal drug delivery has been the subject of multiple scientific investigations, very few attempts have been made to quantitatively relate in vitro and in vivo permeation. The case of naltrexone hydrochloride is not an exception. In the present study, a pharmacokinetic profile obtained following a "poke and patch" microneedle application method in the Yucatan minipig is reported. The profile demonstrates a rapid achievement of maximum naltrexone hydrochloride plasma concentration followed by a relatively abrupt concentration decline. No steady state was achieved in vivo. In an attempt to correlate the present in vivo findings with formerly published in vitro steady-state permeation data, a diffusion-compartmental mathematical model was developed. The model incorporates two parallel permeation pathways, barrier-thickness-dependent diffusional resistance, microchannel closure kinetics, and a pharmacokinetic module. The regression analysis of the pharmacokinetic data demonstrated good agreement with an independently calculated microchannel closure rate and in vitro permeation data. Interestingly, full-thickness rather than split-thickness skin employed in in vitro diffusion experiments provided the best correlation with the in vivo data. Data analysis carried out with the model presented herein provides new mechanistic insight and permits predictions with respect to pharmacokinetics coupled with altered microchannel closure rates.

Design, synthesis and hydrolytic behavior of mutual prodrugs of NSAIDs with gabapentin using glycol spacers

The free –COOH present in NSAIDs is thought to be responsible for the GI irritation associated with all traditional NSAIDs. Exploitation of mutual prodrugs is an approach wherein the NSAID is covalently bounded to a second pharmacologically active carrier/drug with the ultimate aim of reducing the gastric irritation. In this study some NSAIDs were conjugated with gabapentin via ester bonds using glycol spacers with the expectation of reducing gastric adverse effects and obtaining synergistic analgesic effects. The kinetics of ester hydrolysis were studied in two different non enzymatic buffer solutions at pH 1.2 and 7.4, as well as in 80% human plasma using HPLC with chloroform -methanol as mobile phase. Compounds 9a–c with ethylene glycol spacers showed significant stability at buffer solutions with half lives ranging from about 8–25 h, while the underwent a reasonable plasma hydrolysis (49%–88%) in 2 h. Compound 9d with a propylene glycol spacer shows a higher rate of enzymatic hydrolysis than the corresponding ethylene glycol compound 9c. The result of compounds 9a-c indicate that these compounds may be stable during their passage through the GIT until reaching the blood circulation.

Synthesis, characterization and in vitro hydrolysis of a gemfibrozil-nicotinic acid codrug for improvement of lipid profile

Combination therapy of fibrates and nicotinic acid has been reported to be synergistic. Herein, we describe a covalent codrug of gemfibrozil (GEM) and nicotinic acid (NA) that was synthesized and characterized by (1)H NMR, (13)C NMR, FT-IR, MS analysis and elemental analysis. A validated HPLC method was developed that allows for the accurate quantitative determination of the codrug and its hydrolytic products that are formed during the in vitro chemical and enzymatic hydrolysis. The physico-chemical properties of codrug were improved compared to its parent drugs in term of water solubility and partition coefficient. The kinetics of hydrolysis of the codrug was studied using accelerated hydrolysis experiments at high temperatures in aqueous phosphate buffer solution in pH 1.2, 6.8 and 7.4. Using the Arrhenius equation, the extrapolated half-life at 37°C were 289 days at pH 1.2 for the codrug and 130 and 20,315 days at pH 6.8 for the codrug and gemfibrozil 2-hydroxyethyl ester (GHEE), respectively. The shortest half-lives were at pH 7.4; 42 days for the codrug and 5837 days for GHEE, respectively. The hydrolysis of the latter was studied, alone, at 80°C and pH 1.2 and compared to its hydrolysis when it is produced from the codrug using similar conditions. The k(obs) was found in both cases to be 1.60×10(-3)h(-1). The half-lives in plasma were 35.24 min and 26.75 h for the codrug and GHEE, respectively. With regard to liver homogenate, the hydrolysis half-lives were 1.96 min and 48.13 min for the codrug and GHEE, respectively. It can be expected that in vivo, the codrug will liberate NA immediately in plasma then GEM will be liberated from its 2-hydroxyethyl ester in the liver.

Human skin permeation of 3-O-alkyl carbamate prodrugs of naltrexone

N-Monoalkyl and N,N-dialkyl carbamate prodrugs of naltrexone (NTX), an opioid antagonist, were synthesized and their in vitro permeation across human skin was determined. Relevant physicochemical properties were also determined. Most prodrugs exhibited lower melting points, lower aqueous solubilities, and higher oil solubilities than NTX. The flux values from N-monoalkyl carbamate prodrugs were significantly higher than those from NTX and N,N-dialkyl carbamates. The melting points of N-monoalkyl carbamate prodrugs were quite low compared to the N,N-dialkyl carbamate prodrugs and NTX. Heats of fusion for the N,N-dialkyl carbamate prodrugs were higher than that for NTX. N-Monoalkyl carbamate prodrugs had higher stratum corneum/vehicle partition coefficients than their N,N-dialkyl counterparts. Higher percent prodrug bioconversion to NTX in skin appeared to be related to increased skin flux. N,N-Dialkyl carbamate prodrugs were more stable in buffer and in plasma than N-monoalkyl carbamate prodrugs. In conclusion, N-monoalkyl carbamate prodrugs of NTX improved the systemic delivery of NTX across human skin in vitro. N,N-Dialkyl substitution in the prodrug moiety decreased skin permeation and plasma hydrolysis to the parent drug. The cross-sectional area of the carbamate head group was the major determinant of flux of the N-monoalkyl and N,N-dialkyl carbamate prodrugs of NTX.

Drug discovery: phosphinolactone, in vivo bioisostere of the lactol group

In drug discovery, structural modifications over the lead molecule are often crucial for the development of a drug. Herein, we reported the first in vivo bioisosteric effect of phosphinolactone function in relation to the lactol group constituting the bioactive molecule: Hydroxybupropion. The preparation of phosphinolactone analogues and their antidepressant evaluation towards forced swimming test in mice showed that biological activity was regained and even strengthen.

Transdermal delivery of bupropion and its active metabolite, hydroxybupropion: a prodrug strategy as an alternative approach

This investigation includes an evaluation of the percutaneous absorption of bupropion (BUP) and hydroxybupropion (BUPOH) in vitro and in vivo. In addition, a carbamate prodrug of BUPOH (But-BUPOH) was evaluated in vitro. In vitro diffusion studies were conducted in a flow-through diffusion cell system. The in vitro mean steady-state flux of BUP was significantly higher (p < 0.001) compared to BUPOH (320 +/- 16 nmol cm(-2) h(-1) vs. 27 +/- 4 nmol cm(-2) h(-1)). Additionally, a good correlation existed between in vitro and in vivo results. Mean steady-state plasma concentrations of 442 +/- 32 ng/mL and125 +/- 18 ng/mL were maintained over 48 h after topical application of BUP and BUPOH in hairless guinea pigs in vivo, respectively. Although BUP traversed human skin at rates sufficient to achieve required plasma levels, it is chemically unstable and hygroscopic, and unsuitable for transdermal formulation. On the other hand, BUPOH is stable but its transport across skin is much slower. Alternatively, the prodrug But-BUPOH was found to be stable, and also provided a 2.7-fold increase in the transdermal flux of BUPOH across human skin in vitro. Thus, But-BUPOH provides a viable option for the transdermal delivery of BUPOH.

In vivo evaluation of a transdermal codrug of 6-beta-naltrexol linked to hydroxybupropion in hairless guinea pigs

6-Beta-naltrexol is the major active metabolite of naltrexone, NTX, a potent mu-opioid receptor antagonist used in the treatment of alcohol dependence and opioid abuse. Compared to naloxone, NTX has a longer duration of action largely attributed to 6-beta-naltrexol. This study was carried out in order to determine percutaneous absorption of a transdermal codrug of naltrexol, 6-beta-naltrexol-hydroxybupropion codrug (CB-NTXOL-BUPOH), in hairless guinea pigs as well as to evaluate the safety of 6-beta-naltrexol for development as a transdermal dosage form. This codrug may be useful in the simultaneous treatment of alcohol dependence and tobacco addiction. The carbonate codrug traversed the skin at a faster rate than 6-beta-naltrexol. 6-Beta-naltrexol equivalent steady state plasma concentrations of 6.4 ng/ml were obtained after application of the codrug as compared to 1.2 ng/ml from 6-beta-naltrexol base. The steady state plasma concentration of hydroxybupropion after codrug application was 6.9 ng/ml. Skin sensitization and irritation tested in the hairless guinea pigs using the Buehler method revealed that 6-beta-naltrexol had no skin sensitizing potential. The method was validated with a known sensitizer, p-phenylenediamine, which induced sensitization in 90% of the animals. 6-beta-Naltrexol caused only mild transient skin irritation after the initial application of the patch. During subsequent applications, erythema was slightly increased but no skin damage was observed. In conclusion, a transdermal codrug of 6-beta-naltrexol could be a viable alternative treatment for alcohol and opiate abuse.

Comparison of naltrexone, 6alpha-naltrexol, and 6beta-naltrexol in morphine-dependent and in nondependent rhesus monkeys

RATIONALE

Some opioid receptor ligands that appear to be neutral antagonists can have inverse agonist activity under conditions of increased constitutive activity (e.g., agonist treatment).

OBJECTIVES

This study compared the opioid receptor antagonist naltrexone and its metabolites 6alpha-naltrexol and 6beta-naltrexol in nondependent and morphine-dependent monkeys to see whether their potencies varied according to drug treatment and, presumably, to differences in constitutive activity of mu opioid receptors.

RESULTS

In monkeys (n = 4) receiving 3.2 mg/kg per day of morphine and discriminating 0.0178 mg/kg naltrexone, naltrexone and each metabolite increased responding on the naltrexone lever in a dose-related manner with naltrexone being 8- and 71-fold more potent than 6alpha- and 6beta-naltrexol, respectively. After 27 h of no-morphine treatment, monkeys responded on the naltrexone lever, and this effect was reversed by morphine. Naltrexone and each metabolite prevented morphine reversal of naltrexone-lever responding, and their rank order potency was the same as their substitution for naltrexone; however, the potency between naltrexone and each metabolite was slightly greater in morphine-dependent as compared to morphine-deprived monkeys. In a separate group (n = 3) of nondependent monkeys discriminating 1.78 mg/kg of morphine, all three compounds antagonized morphine with the same potency as in the reversal study (morphine-dependent monkeys), with Schild analyses showing no difference in apparent affinities (pA (2)) between nondependent and morphine-dependent monkeys.

CONCLUSION

Naltrexone and 6alpha- and 6beta-naltrexol have qualitatively similar effects, and their potencies do not vary markedly with opioid treatment, suggesting that under these conditions, they do not vary with regard to inverse agonism.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Phase I and phase II ocular metabolic activities and the role of metabolism in ophthalmic prodrug and codrug design and delivery

While the mammalian eye is seldom considered an organ of drug metabolism, the capacity for biotransformation is present. Compared to the liver, the metabolic capabilities of the eye are minuscule; however, phase I and phase II metabolic activities have been detected in various ocular structures. The careful consideration of ocular tissue metabolic processes within the eye has important implications for controlling the detoxification of therapeutic agents and for providing the potential for site-specific bio-activation of certain drug molecules, thus enabling significant improvements in drug efficacy and the minimization of side-effect from either local or systemic drug delivery to the eye. Knowledge of these processes is important to prodrug and codrug development and to researchers involved in the design, delivery and metabolism of ophthalmic drugs. This present article reviews the progress in ocular prodrug and codrug design and delivery in light of ocular metabolic activities.