Hydroxymethyl and acyloxymethyl prodrugs of theophylline: enhanced delivery of polar drugs through skin

A series of 7-acyloxymethyl prodrugs of theophylline has been prepared by the acylation of 7-(hydroxymethyl)theophylline and by the alkylation of theophylline with an acyloxymethyl halide. The lipid solubilities of all the prodrugs were markedly improved over that of theophylline but, in addition, the succinamate and the glycinate derivatives exhibited increased water solubilities. As a result, prodrugs which exhibited partition coefficients between 0.03 and 16.7 were obtained. Selected acyloxymethyl prodrugs as well as 7-(hydroxymethyl)theophylline were effective in increasing the delivery of theophylline through hairless mouse skin by 3.5–5 times that of theophylline. Several of the prodrugs, when applied topically to normal and hairless mice, inhibited DNA synthesis in the skins of the mice after they had undergone UV irradiation.     

Evaluation of antimicrobial activities of several mannich bases and their derivatives

The aim of this study was to evaluate the antimicrobial activities of several Mannich bases and their derivatives against pathogenic bacteria and fungi. 3-Dimethylamino-1-phenyl-1-propanone hydrochloride (Ig1) as mono-Mannich base, bis(beta-aroylethyl)methylamine hydrochlorides (B1, B5) as bis-Mannich bases, 3-aroyl-4-aryl-1-methyl-4-piperidinol hydrochlorides (C1, C5) as piperidinol derivatives, which are structural isomers of bis-Mannich bases, N,N'-Bis(3-dimethylamino-1-phenylpropylidene)hydra zine dihydrochlorides (D1) as azine derivative of mono-Mannich base Ig1, and some representative quaternary derivatives (Ig4 and C6), which are quaternary derivatives of Ig1 and C1, respectively, have been synthesized. Aryl parts were phenyl in B1 and C1, and 2-thienyl in B5 and C5. Bis-Mannich bases and quaternary Mannich bases were found to be effective antifungal derivatives. Quaternary mono-Mannich base Ig4 has shown twice the amount of higher antifungal potency against the human pathogenic fungus Microsporum canis compared with the reference drug amphotericin-B and it had equal potency against many other fungi species pathogenic in humans and plants. Ig4 was effective against Staphylococcus aureus among the bacteria tested. Preparation of bis-Mannich bases and qua ternization procedure seemed suitable chemical modifications to prepare effective antifungal compounds. Especially quaternary derivatives Ig4, and to some extent C6, seem to be model compounds to develop new antimicrobial agents for further studies.     

Antifungal activity of some mono, bis and quaternary Mannich bases derived from acetophenone

The development of resistance to current antifungal therapeutics drives search for new effective agents. Some Mannich bases have antifungal activity, but no information is available regarding the antifungal activity of acetophenone derived Mannich bases. Mono Mannich bases of acetophenone 1-3 were synthesized and converted into their corresponding bis derivatives, 5-7. Representative quaternary derivatives 4 and 8 were also synthesized. Antifungal activities of the compounds were evaluated using some yeasts and dermatophytes in vitro. Mono Mannich base 3 and quaternary compounds 4 and 8 were found to be 2-16 times more potent than the reference compound amphotericin B against dermatophytes: Trichophyton rubrum, Trichophyton mentagrophytes, and Microsporum canis. Compounds 4 and 8 were also found to be 2 times more effective compared with amphotericin B against the yeast Saccharomyces cerevisiae. Quaternization procedure improved the biological activity dramatically, whereas conversion of mono Mannich bases to corresponding bis derivatives generally did not affect antifungal activity. Our results suggest that acetophenone derived mono Mannich base 3 and quaternary derivatives 4 and 8 may serve as leading compounds for further studies to develop new antifungal agents with their highly potent antifungal activity.     

Cytotoxic activities of some mono and bis Mannich bases derived from acetophenone in brine shrimp bioassay

Some mono Mannich bases (1-phenyl-3-amino-1-propanone salts) and bis Mannich bases (1-phenyl-3-amino-2-amino-methyl-1-propanone salts) derived from acetophenone and a few representative quaternary derivatives were synthesised and their cytotoxicity was tested using the brine shrimp bioassay. This assay may serve as an intermediate test before further in vivo animal experiments in large scale, since brine shrimp nauplii as whole organisms were used in this test. Mono Mannich bases were generally more cytotoxic than their corresponding bis Mannich bases. Mannich bases synthesised were cytotoxic in both brine shrimp bioassay in this study and cell culture tests using Jurkat and Renca cells in a previous study. However, the order of the cytotoxic potency of the compounds were reverse, which may result from faster deamination of bis derivatives than optimal level, and different species and test media used in the two test systems. Faster deamination of bis derivatives might have led to elimination of active metabolites before reaching its target. The cytotoxicity of the compounds might have been altered by amino acids and proteins present in cell culture medium but not in sea water used in brine shrimp bioassay affecting their transport through the cell membrane and metabolism in the cell by binding with the compounds. With higher cytotoxic activity compared with 5-fluorouracil (CAS 51-21-8) in brine shrimp bioassay, mono Mannich base 1 and its quaternary derivative 4 and quaternary bis derivative 8 seem to be candidate compounds for further drug design.     

Prodrugs of 5-fluorouracil. IV. Hydrolysis kinetics,bioactivation and physicochemical properties of various N-acyloxymethyl derivatives of 5-fluorouracil

The kinetics and mechanism of hydrolysis of various 1-, 3- and 1,3-acyloxymethyl derivatives of 5-fluorouracil were studied to assess their potential as prodrugs with the aim of enhancing the delivery characteristics of the parent drug. All the derivatives hydrolyzed to yield 5-fluorouracil in quantitative amounts, passing through an unstable N-hydroxymethyl-5-fluorouracil intermediate. The pH-rate profiles obtained revealed the occurrence of specific acid and base catalysis as well as of a water-catalyzed reaction. The rates of hydrolysis were accelerated markedly in the presence of human plasma or rat liver homogenate, suggesting the utility of the derivatives as prodrugs. The derivatives were all more lipophilic than 5-fluoro-uracil as determined by partition experiments in octanol-aqueous buffer systems but the aqueous solubility was only slightly reduced or, for some derivatives, even greater than that of 5-fluorouracil. This behaviour was attributed to differences in the crystal lattice energy, and relationships between melting points, partition coefficients and water-solubilities for these and 11 other prodrug derivatives of 5-fluoro-uracil were established.     

Synthesis, physicochemical properties and biological evaluation of aromatic ester prodrugs of 1-(2'-hydroxyethyl)-2-ethyl-3-hydroxypyridin-4-one (CP102): orally active iron chelators with clinical potential.

The synthesis of seven aromatic ester derivatives of 1-(2'-hydroxyethyl)-2-ethyl-3-hydroxypyridin-4-one is described. These ester prodrugs have been designed to target iron chelators to the liver, the major iron storage organ. In principle this should improve chelation efficacy and minimize toxicity. The distribution coefficients of these ester prodrugs between 1-octanol and MOPS buffer pH 7.4 were measured together with their rates of hydrolysis at pH 2 and pH 7.4, in rat blood and liver homogenate. Esters with heteroaromatic acid moieties were found to be less stable than benzoyl analogues. The in-vivo iron mobilisation efficacy of these ester prodrugs has been compared with that of the parent drug using a 59Fe-ferritin loaded rat model. Many prodrugs were found to enhance the ability of the parent hydroxypyridinone to facilitate 59Fe excretion. However, not all prodrugs provided increased efficacy, demonstrating that lipophilicity is not the only factor which influences drug efficacy. Furthermore, no clear correlation between efficacy and susceptibility to hydrolysis was detected. The picolinic and nicotinic ester derivatives appear to offer the best potential as prodrugs as they have a relatively low LogP value and yet lead to enhanced efficacy over the parent hydroxypyridinone.     

N-(Acyloxyalkoxycarbonyl) derivatives as potential prodrugs of amines. II. esterase-catalysed release of parent amines from model prodrugs

N-(Acetoxyethoxycarbonyl) derivatives of primary amines released a major fraction of the parent amine in the desired free form in plasma but a significant fraction of the undesired N-acetylated parent amine was also produced. The fraction of the parent amines released from the carbamate derivatives of the primary amines was greater in human plasma than in pH 7.4 buffer. In human plasma, the N-(acetoxyethoxycarbonyl) derivative of a secondary amine released the parent amine in a quantitative manner at a rate higher than that observed in pH 7.4 buffer. Experimental results suggested that the observed catalysis of the release of the parent amines from N-(acetoxyethoxycarbonyl) derivatives of primary and secondary amines was due to participation by plasma esterases. The data suggested that N-(acetoxyethoxycarbonyl) derivatives are well suited for use as prodrugs of secondary amines. Their utility as prodrugs of primary amines is more problematic and cannot be predicted prior to in-vivo studies for the individual compound.     

Pharmacological and biochemical activities of some monomethylxanthine and methyluric acid derivatives of theophylline and caffeine.

Some monomethylxanthine and methyluric acid derivatives of theophylline and caffeine have been studied to explore whether they possess pharmacological and biochemical activities similar to those of their parent compounds. Both 3-methylxanthine and 1-methylxanthine, but not 1,3-dimethyluric acid or 3-methyluric acid, produced the same maximal relaxation of guinea pig tracheal muscle as did theophylline. The EC₅₀ values for theophylline and 3-methylxanthine were not significantly different, whereas those for 1-methylxanthine, 1,3-dimethyluric acid and 3-methyluric acid were significantly higher than that if theophylline. In the Langendorff guinea pig heart, theophylline and 3-methylxanthine caused essentially identical increases in cardiac contractile force. Although less effective than theophylline, 1-methylxanthine and caffeine produced equivalent increases in cardiac contractility. At concentrations higher than those effective for the methylxanthines, 1,3-dimethyluric acid markedly increased contractile force. 3-Methylxanthine inhibited cyclic AMP phosphodiesterase to a lesser extent than did theophylline at both 1.4 and 400 μM cyclic nucleotide concentrations. However, at the higher substrate concentration, cyclic GMP phosphodiesterase activity was inhibited by 3-methylxanthine more than by theophylline. Thus, it appears that the monomethylxanthine and methyluric acid derivatives of theophylline and caffeine possess a spectrum of pharmacological activity similar to that of their parent compounds, a finding which raises important questions about various aspects of the current therapeutic use of methylxanthines.     

Development of lipophilic prodrugs of mitomycin C. II. Stability and bioactivation of 1a-N-substituted derivatives with aromatic pro-moiety

The decomposition and bioactivation characteristics of five la-N-substituted derivatives of mitomycin C possessing an aromatic pro-moiety with different linkage structures were studied to assess their suitability for prodrugs. Derivatives were stable in neutral aqueous media except for benzoyloxymethyl mitomycin C which decomposed with a half-life of 3.5 min at pH 7.4. Acyl derivatives such as benzoyl and benzylcarbonyl mitomycin C were stabler than mitomycin C under acidic conditions, but converted relatively rapidly to the parent drug in basic media. Derivatives having an ester bond in their linkages showed enzyme-mediated conversion to the parent drug in rat plasma and liver homogenate. Acyl derivatives were converted only by hepatic enzymes. No practical bioactivation was observed for benzyl mitomycin C. Species differences were observed in these bioactivation phenomena. These results suggested that 5 derivatives have intrinsic regeneration characteristics which might offer successful applications under various conditions of administration.     

New MultiPEG-conjugated theophylline derivatives: synthesis and pharmacological evaluations.

The successful conjugation of active theophylline molecules to two new multifunctional high-molecular weight poly(ethylene glycol) derivatives (MultiPEG) and their pharmacokinetic evaluations are reported. The drug loading was increased up to six times in comparison with commercial PEG of the same molecular weight. A clear increase of the time of persistence within the body and a concomitant improvement of the overall pharmacokinetic properties of those prodrugs were also observed. These studies sustain the use of these new PEG-based polymeric supports as a valuable alternative for an effective drug delivery system.     

Chemical and enzymatic stability evaluation of lipoamino acid esters of idebenone.

Lipophilic conjugates of idebenone (IDE) with short-chain alkylamino acids were previously synthesized and evaluated in vitro for their antioxidant properties. In this study, their susceptibility to chemical and enzymatic hydrolysis was evaluated. Results indicated that these derivatives release the parent drug quantitatively via enzymatic hydrolysis by serum and liver esterases, with a cleavage rate related to the length of the alkyl side chain. Consequently, the present lipoamino acid conjugates of IDE are prodrugs and their in vivo effects are mediated through the parent compound released in the body.     

木犀草素Mannich碱衍生物的合成及其抗癌活性

目的:合成木犀草素Mannich碱衍生物并考察其抗癌活性。方法:室温下木犀草素与甲醛、胺经Mannich反应得到8种Mannich碱衍生物。采用MTT法,以5氟-尿嘧啶(5-Fu)为阳性对照药,通过人宫颈癌细胞(Hela)、人胃癌细胞(SGC-7901)、人结肠癌细胞(HCT-116)、人白血病细胞(K562)、人乳腺癌细胞(MCF-7)、人前列腺癌细胞(DU-145)等6种肿瘤细胞进行体外抗癌活性评价,以正常人胚肾上皮细胞(HEK-293)为毒性对照;对化合物8h进行抗癌分子机制研究。结果:合成的8种化合物结构经1H-NMR、13C-NMR和MS确证。体外抗癌活性试验表明部分化合物显示出比木犀草素更好的抗癌活性。结论:化合物8h可能通过线粒体途径抑制SGC-7901细胞增殖,从而诱导细胞凋亡。     

Prodrugs of 5-fluorouracil. V. 1-Alkoxycarbonyl derivatives as potential prodrug forms for improved rectal or oral delivery of 5-fluorouracil

The hydrolysis and physicochemical properties of seven 1-alkoxycarbonyl derivatives of 5-fluorouracil were studied to assess their potential as prodrugs with the aim of enhancing the delivery characteristics of the parent drug. All derivatives were hydrolyzed to quantitatively yield 5-fluorouracil. The pH-rate profiles for the hydrolysis were measured. The rates of hydrolysis were markedly accelerated in the presence of plasma, affording half-lives of hydrolysis less than 4 min in 80% human plasma. The derivatives were more lipophilic than 5-fluorouracil but the aqueous solubility was only slightly reduced or, for one derivative, even greater than that of 5-fluorouracil. A preliminary absorption study in rabbits showed an absolute bioavailability of 5-fluorouracil of 100% following rectal administration of 1-(butoxycarbonyl)-5-fluorouracil as compared with no absorption following administration of 5-fluorouracil itself. The potential utility of the prodrug derivatives to enhance the oral and/or rectal delivery of the parent drug is suggested.     

Effect of aminomethyl (N-Mannich base) derivatization on the ability of S6-acetyloxymethyl-6-mercaptopurine prodrug to deliver 6-mercaptopurine through hairless mouse skin

A series of 9-aminomethyl-S6-acetyloxymethyl-6-mercaptopurine (9-AM-6-AOM-6-MP) prodrugs have been synthesized and characterized, and their ability to deliver total 6-mercaptopurine (6-MP) through hairless mouse skin has been measured. The 9-AM-6-AOM-6-MP prodrugs are much more soluble in isopropyl myristate (IPM) than S6-acetyloxymethyl-6-MP (6-AOM-6-MP) itself or the corresponding 7-aminomethyl-6-MP (7-AM-6-MP) prodrugs. The 9-AM-6-AOM-6-MP prodrugs were all more effective (1.8-4 times) than 6-AOM-6-MP at delivering total 6-MP, except for the piperidylmethyl derivative which only gave a comparable rate of delivery. The 9-AM-6-AOM-6-MP prodrugs were also more effective (7-27 times) than the corresponding 7-AM-6-MP prodrugs at delivering 6-MP, except for the diethylaminomethyl derivative which only gave a comparable rate of delivery. In contrast to the 9-aminomethyl-S6-pivaloyloxymethyl-6-MP (9-AM-6-POM-6-MP) derivatives which generally delivered as much or more intact S6-pivaloyloxymethyl-6-MP (6-POM-6-MP) as 6-MP, the 9-AM-6-AOM-6-MP derivatives delivered mainly (80-95%) 6-MP from IPM. There was a direct correlation between log experimental permeability coefficients for delivery of total 6-MP (P sigma) and the calculated solubility parameter values for the 9-AM-6-AOM-6-MP prodrugs(delta j), with the P sigma generally decreasing as the value of delta j approached that of the vehicle, IPM.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acyloxymethyl acidic drug derivatives: in vitro hydrolytic reactivity

A series of acyloxymethyl drug derivatives of the NH-acidic drugs, phenytoin and theophylline and of the carboxylic acid drugs, thioctic acid and indomethacin, were prepared in order to determine the effect of varying the nature of the drug on the in vitro rate of hydrolysis catalyzed by porcine liver esterase and human plasma. The acyl portion was comprised of either valeric acid (val) or γ-linolenic acid (GLA). With the exception of some GLA prodrugs, the derivatives displayed first-order kinetics in both enzyme systems. The NH-acidic drug derivatives were hydrolyzed faster than the carboxylic drug derivatives by porcine liver esterase and human plasma. It was found that the short chain valeric acid derivatives were hydrolyzed faster than the GLA derivatives. The rates of hydrolysis for the relatively smaller prodrugs of theophylline and thioctic acid were greater than the rates of hydrolysis for the bulkier phenytoin and indomethacin prodrugs indicating steric hindrance was important. The lipophilicity index, log K, of the valeric acid drug derivatives was plotted against the logarithm of the hydrolysis rate constant, k, and it was observed that log k decreased with an increase in log K. A comparison of these results with those of previous studies where the alkyl and acyl moieties were varied of acyloxyalkyl theophylline derivatives has provided a rationale, based on lipophilicity, for the structure of a prodrug to be designed based on an in vitro desired rate of hydrolysis.     

麻黄生物碱衍生物噁唑烷的合成与前药研究

用三种麻黄碱和芳醛反应合成28个2-芳基-3,4-二甲基-5-苯基噁唑烷类和Schiff碱类化合物。根据前药原理用UV和HPLC法探讨了立体结构和水解动力学的问题,测得生理条件下的水解半寿期,初步阐明了空间效应对稳定性的影响以及Hammett取代基常数与水解速率的规律。实验表明此类噁唑烷衍生物作为麻黄碱的前药有理论和应用价值。     

Aminocarbonyloxymethyl ester prodrugs of flufenamic acid and diclofenac: suppressing the rearrangement pathway in aqueous media

Aminocarbonyloxymethyl ester prodrugs are known to undergo rearrangement in aqueous solutions to form the corresponding N-acylamine side product via an O-->N intramolecular acyl transfer from the carbamate conjugate base. Novel aminocarbonyloxymethyl esters of diclofenac and flufenamic acid containing amino acid amide carriers were synthesized and evaluated as potential prodrugs displaying less ability to undergo rearrangement. These compounds were prepared in reasonable yield by a four-step synthetic method that uses the appropriate N-Boc-protected amino acid N-hydroxysuccinimide ester and secondary amine and chloromethyl chloroformate as key reactants. Their reactivity in pH 7.4 buffer and 80% human plasma at 37 degrees C was assessed by RP-HPLC. The aminocarbonyloxymethyl esters containing a secondary carbamate group derived from amino acids such as glycine or phenylalanine were hydrolyzed quantitatively to the parent drug both in non-enzymatic and enzymatic conditions, with no rearrangement product being detected. The oral bioavailability in rats was determined for selected diclofenac derivatives. These derivatives displayed a bioavailability of 25 to 68% relative to that of diclofenac, probably due to their poor aqueous solubility and lipophilicity. These results suggest that further optimization of aminocarbonyloxymethyl esters as potential prodrugs for non-steroidal anti-inflammatory drugs require the use of amino acid carriers with ionizable groups to improve aqueous solubility.     

Alkylation of 6-mercaptopurine (6-MP) with N-alkyl-N-alkoxycarbonylaminomethyl chlorides: S6-(N-alkyl-N-alkoxycarbonyl)aminomethyl-6-MP prodrug structure effect on the dermal delivery of 6-MP

The S6-(N-alkyl-N-alkoxycarbonyl)aminomethyl-6-MP (6-CARB-6-MP) prodrugs 5-20 were synthesized from the reaction of 6-MP with N-alkyl-N-alkyoxycarbonylaminomethyl chlorides (4) in dimethyl sulfoxide in overall yields of 5-62%, depending on the N-alkyl and the alkoxy groups involved. The derivatives were fully characterized by spectral and microanalyses. The assignment of the substitution pattern as S6-alkyl was based on comparisons of the UV, 1H NMR and 13C NMR spectra with model compounds. A S6, 9-bis-alkyl derivative was obtained from the reaction of 2 equivalents of 4 with 6-MP but the product was unstable and decomposed on standing to a 9-alkyl derivative. The 6-CARB-6-MP prodrugs reverted to 6-MP in water by an SN1-type mechanism involving unimolecular charge separation in the transition state of the rate determining step. There was no effect of dermal enzymes on the rate of hydrolysis. The solubilities in isopropyl myristate (IPM) for all of the 6-CARB-6-MP prodrugs were significantly greater than the solubility of 6-MP in IPM but only one prodrug (5) was apparently even as soluble as 6-MP in water. Selected 6-CARB-6-MP prodrugs were examined in diffusion cell experiments. Only the N-methyl-N-methoxycarbonyl derivative 5 gave a steady-state rate of delivery of 6-MP from IPM that was significantly greater than the steady-state rate of delivery of 6-MP from 6-MP in IPM. All the other derivatives gave steady-state rates of delivery of 6-MP from IPM that were either not significantly different, or were significantly lower than the rate obtained from 6-MP in IPM. In all cases, the effect of the 6-CARB-6-MP:IPM suspensions on the permeability of the skin, as determined by the second application flux of theophylline:propylene glycol, was of the same magnitude as the effect of IPM alone.     

In vitro evaluation of acyloxyalkyl esters as dermal prodrugs of ketoprofen and naproxen

A series of acyloxyalkyl esters of ketoprofen and naproxen were synthesized and investigated as topical prodrugs with the aim of improving the dermal delivery of the drugs. In addition, some hydroxyalkyl esters of ketoprofen and naproxen were synthesized as possible intermediates of acyloxyalkyl prodrugs. All of the prodrugs were more lipophilic than their parent molecules, as evaluated by drug partitioning between 1-octanol and phosphate buffer at pH 7.4 (log Papp). However, their solubilities in aqueous solutions decreased markedly compared with the parent molecules. The prodrugs were stable toward chemical hydrolysis in aqueous solutions (pH 7.4), but were hydrolyzed to the parent drug both in 80% human serum and in human skin homogenate, with half-lives ranging from 4 to 137 min and from 13 to 403 min, respectively. The abilities of the selected naproxen acyloxyalkyl prodrugs to deliver naproxen through excised human skin were evaluated. Generally, the prodrugs showed similar dermal delivery as the parent drug through cadaver skin. In the present series of lipophilic prodrugs of naproxen, the prodrug with the highest aqueous solubility was the most effective prodrug to deliver naproxen through the skin.     

Synthesis, DNA affinity, and antiprotozoal activity of fused ring dicationic compounds and their prodrugs

Dicationic guanidine, N-alkylguanidine, and reversed amidine derivatives of fused ring systems have been synthesized from their corresponding bis-amines. DNA binding studies suggest that the diguanidines and the N-alkyl diguanidines fluorenes bind in the minor groove in a manner similar to that of the previously reported dicationic carbazole derivatives. The diguanidines and the N-alkyl diguanidines showed promising in vitro activity against both Trypanosoma brucei rhodesiense and Plasmodium falciparum. Promising in vivo biological results were obtained for the dicationic N-isopropylguanidino-9H-fluorene, giving 4/4 cures of the treated animals in the STIB900 animal model for African trypanosomiasis. The N-methyl analogue showed high activity as well. In addition, with the goal of enhancing the oral bioavailability, two novel classes of potential guanidine prodrugs were prepared. The N-alkoxyguanidine derivatives were not effective as prodrugs. In contrast, a number of the carbamates showed promising activity. The value of the carbamate prodrugs was clearly demonstrated by the results, which gave 4/4 cures on oral administration in the STIB900 mouse model.