Antimalarial and anticancer activities of artemisinin-quinoline hybrid-dimers and pharmacokinetic properties in mice.

Malaria, one of the three most important life-threatening infectious diseases, is recommended to be treated with ACT (artemisinin combination therapy) against which Plasmodium falciparum already displayed resistance. Two artemisinin-4-amino-quinoline hybrid-dimers (1 and 2), previously synthesized, possessed low nanomolar in vitro antiplasmodial activity, while poorly toxic against mammalian cells. They are here investigated to ascertain whether this antimalarial activity would be carried on in vivo against Plasmodium vinckei. During the four day treatment, parasitemia of less than 1% were observed on day 5 after doses from 2.5 mg/kg ip and 50 mg/kg po for hybrid-dimer 1, and from 7.5 mg/kg ip and 25 mg/kg po for hybrid-dimer 2. Snapshot pharmacokinetic analysis demonstrated that the antiplasmodial activity of these C-10-acetal artemisinin dimers may be due to active metabolites, which were confirmed by in silico findings. Hybrid-dimer 1 also displayed potent in vitro activity against tumor cells and was found to be more active than etoposide against TK10, UACC62 and MCF7 cell lines (TGI values 3.45 vs. 43.33 µM, 2.21 vs. 45.52 µM and 2.99 vs. >100 µM, respectively). The 1,3-diaminopropane linker, present in hybrid-dimer 1, was therefore identified as the optimum linker.

Synthesis and in vitro antimalarial activity of a series of bisquinoline and bispyrrolo[1,2a]quinoxaline compounds.

Series of bisquinolines 4-15 and bispyrrolo[1,2a]quinoxalines 16-20 containing various polyamine linkers were synthesized. The aqueous solubility and distribution coefficient were experimentally determined. The compounds were screened for antimalarial activity alongside chloroquine against D10 and Dd2 strains of Plasmodium falciparum. The growth inhibitory effects of biscompounds 4-9 were assessed against various cancer cell lines. The aqueous solubility was found to increase with an increase in potential protonation sites. Bisquinolines 8 and 9 featuring triethylenetetramine and N,N'-bis(3-aminopropyl)ethylene-diamine linkers, respectively, were the most active of all synthesized compounds. They were found as potent as chloroquine against D10 but significantly more potent against the Dd2 strain, with good selectivity towards parasitic cells. Compound 4 containing a diethylenetriamine bridge displayed the most important anticancer activity of the series, and was a more effective antiproliferative inhibitor than etoposide against all three TK10, UACC62 and MCF7 cancer cell lines.

Synthesis, antimalarial activity and cytotoxicity of 10-aminoethylether derivatives of artemisinin.

In this study, a series of 11 10-aminoethylether derivatives of artemisinin were synthesised and their antimalarial activity against both the chloroquine sensitive (D10) and resistant (Dd2) strains of Plasmodium falciparum was determined. The compounds were prepared by introducing aliphatic, alicyclic and aromatic amine groups with linkers of various chain lengths through an ethyl ether bridge at C-10 of artemisinin using conventional and microwave assisted syntheses, and their structures were confirmed by NMR and HRMS. All derivatives proved to be active against both strains of the parasite. The highest overall activity was displayed by the short chain aromatic derivative 8 (IC(50)=1.44nM), containing only one nitrogen atom, while long chain polyamine derivatives were found to have the lowest activity against both strains. An interesting correlation between the IC(50), pK(a) values and resistance index (RI) was found.

Synthesis and in vitro antiplasmodial activity of quinoline-ferrocene esters.

New 4-aminoquinoline-derived esters containing the redox-active ferrocene group brought in by either ferrocenyformic or 4-ferrocenylbutanoic acids were synthesized and tested in vitro for their antiplasmodial activity. The results revealed that only esters derived from ferrocenylformic acid were active against both chloroquine (CQ)-resistant Dd2 and CQ-sensitive D10 strains of Plasmodium falciparum. However, none of these showed higher actvity than CQ against the sensitive strain. Ester 16, which possesses a butyl branch in the structure, was the most active of all. With an IC50 of 0.13 mM on the resistant strain, this ester possessed 2.5-fold higher activity than CQ (IC50 = 0.34 mM). All tested esters showed good selectivity towards P. falciparum with indexes higher than 60.

Mono-, di- and trisubstituted derivatives of eflornithine: synthesis for in vivo delivery of DL-alpha-difluoromethylornithine in plasma.

The aim of this study was to synthesize a series of mono-, di- and trisubstituted derivatives of the human African trypanosomiasis drug eflornithine (alpha-difluoromethylornithine, DMFO, CAS 70052-12-9) to determine their partition coefficients, and to assess whether they deliver the parent drug in the plasma. If increased plasma concentrations of eflornithine could be achieved in this way, an oral dosage form would be possible. The derivatives, nine in total, were successfully synthesized by multi-step derivatisation of eflornithine on either its alpha-carboxylic or/and alpha-amino or/and delta-amino groups by either esterification or/and amidation or/and carbamylation, and their structures confirmed by NMR and MS spectroscopy. The majority of derivatives were more lipophilic than eflornithine with log D values in phosphate buffer solution (pH 7.4) ranging from -1.34 to 1.59 (vs. -0.98 for eflornithine). The in vivo absorption after oral administration to Sprague-Dawley rats showed that no derivative delivered eflornithine in the plasma, indicating that the derivatives were either not absorbed from the gastrointestinal tract or not metabolized to the parent drug. Two of the monosubstituted activities were toxic for T. brucei blood stream forms.

Synthesis, in vitro antimalarial and cytotoxicity of artemisinin-aminoquinoline hybrids.

Dihydroartemisinin (DHA) was coupled to different aminoquinoline moieties forming hybrids 9-14, which were then treated with oxalic acid to form oxalate salts (9a-14a). Compounds 9a, 10a, 12, 12a, and 14a showed comparable potency in vitro to that of chloroquine (CQ) against the chloroquine sensitive (CQS) strain, and were found to be more potent against the chloroquine resistant CQR strain. Hybrids 12 and its oxalate salt 12a were the most active against CQR strain, being 9- and 7-fold more active than CQ, respectively (17.12 nM; 20.76 nM vs 157.9 nM). An optimum chain length was identified having 2 or 3 Cs with or without an extra methylene substituent.

Synthesis and antimalarial activity of ethylene glycol oligomeric ethers of artemisinin.

OBJECTIVES: The aim of this study was to synthesize a series of ethylene glycol ether derivatives of the antimalarial drug artemisinin, determine their values for selected physicochemical properties and evaluate their antimalarial activity in vitro against Plasmodium falciparum strains. METHODS: The ethers were synthesized in a one-step process by coupling ethylene glycol moieties of various chain lengths to carbon C-10 of artemisinin. The aqueous solubility and log D values were determined in phosphate buffered saline (pH 7.4). The derivatives were screened for antimalarial activity alongside artemether and chloroquine against chloroquine-sensitive (D10) and moderately chloroquine-resistant (Dd2) strains of P. falciparum. KEY FINDINGS: The aqueous solubility within each series increased as the ethylene glycol chain lengthened. The IC50 values revealed that all the derivatives were active against both D10 and Dd2 strains. All were less potent than artemether irrespective of the strain. However, they proved to be more potent than chloroquine against the resistant strain. Compound 8, featuring three ethylene oxide units, was the most active of all the synthesized ethers. CONCLUSIONS: The conjugation of dihydroartemisinin to ethylene glycol units of various chain lengths through etheral linkage led to water-soluble derivatives. The strategy did not result in an increase of antimalarial activity compared with artemether. It is nevertheless a promising approach to further investigate and synthesize water-soluble derivatives of artemisinin that may be more active than artemether by increasing the ethylene glycol chain length.

Synthesis, cytotoxicity and antimalarial activity of ferrocenyl amides of 4-aminoquinolines.

Series of 4-aminoquinolines bearing an amino side chain linked to the ferrocene moiety through an amide bond were synthesized and evaluated for their antimalarial activity against both chloroquine-sensitive (D10, CQ-S) and chloroquine-resistant (Dd2, CQ-R) strains of Plasmodium falciparum. They were also tested for cytotoxicity against Chinese Hamster Ovarian (CHO) cells. Amide 12 featuring propyl side chain linked to the ferrocene ring was the most active of all tested compounds. With an IC50 value of 0.08 microg/mL, this amide showed 1.5-fold higher activity than chloroquine diphosphate (IC50 = 0.12 microg/mL) against the resistant strain, with a selectivity index of 550 indicating its high selectivity towards the parasite. Derivatives which were equipotent against both strains also showed up to ten-fold increase in activity compared to primaquine.

Synthesis and in vitro human skin penetration of oligo- and polymeric ethylene glycol carbonates of zidovudine and stavudine.

In continuation of studies focusing on the transdermal delivery of antiretroviral (ARV) drugs, the skin permeation ability of synthesized homologous series of both oligomeric and polymeric ethylene glycol (PEG) carbonates of zidovudine (3'-azido-3'-deoxythymidine, AZT, CAS 30516-87-1) and stavudine (2',3'-dideoxy-2',3'-didehydrothymine, d4T, CAS 3056-17-5) was evaluated in vitro through excised human skin in phosphate buffered solution (PBS) (0.01 M, pH 7.4) at 37 degrees C by using Franz cell diffusion methodology. The results revealed that all the derivatives permeated the skin regardless of the series. However, the derivative having three ethylene glycol repeating units was the most effective permeant in each series. The skin permeation rates of zidovudine and stavudine were enhanced by factors in the 2-4, and 1-3 range through these carbonates, respectively.

Effects of oral administration of synthesized delta-amides of eflornithine in the rat.

The purpose of this study was to synthesize a series of delta-amide derivatives of the antitrypanosomal drug eflornithine (2,5-diamino-2-(difluoromethyl)pentanoic acid hydrochloride, DMFO, CAS 70052-12-9), to determine their physicochemical properties and to assess whether they convert to eflornithine in vivo and if so, whether higher systemic exposure to eflornithine could be achieved by increase intestinal absorption, suggesting an oral treatment to be possible. The derivatives were synthesized by amidation of eflornithine on its delta-amino group using acyl chlorides. The partition coefficients (log D, pH = 7.4) were found to be between -0.78 +/- 1.07 and -0.07 +/- 1.08 while the aqueous solubility (Sw), which as determined in phosphate buffered solution (pH 7.4), ranged from 11.13 +/- 0.32 to 28.74 +/- 0.36 mg/mL. The synthesized compounds were thus mostly more lipophilic than eflornithine itself (log D = -0.98 +/- 0.88, Sw = 34.96 +/- 0.37 mg/mL). The intestinal absorption was assessed by plasma analysis after oral administration of each compound to Sprague-Dawley rats. The biological data revealed that the derivatives were either not absorbed from the gastro-intestinal tract or not metabolized into eflornithine as no parent drug was detected in the plasma.

Synthesis and transdermal penetration of stavudine-5'-esters.

The aim of this study was to investigate the effects of different ester groups in position 5' of stavudine on the transdermal penetration with and without the use of Pheroid™ as the delivery system. Six esters were prepared by reaction of stavudine with six different acid chlorides at room temperature. Female human abdominal skin was used for in vitro penetration in Franz diffusion cells. The experimental aqueous solubility of stavudine (104.75 mg/mL) was much higher than that of the synthesized derivatives (ranging from 0.08 to 5.17 mg/mL), while the log D (octanol-buffer partition coefficient) of stavudine (-0.85) was lower than that of its derivatives (ranging from -0.41 to 3.06). The experimental transdermal flux of stavudine (6.52 µmol/cm(2).h) in PBS (phosphate buffer solution) was much higher than that of any of its derivatives (0.06 - 0.23 µmol/cm(2).h), while the propionyl (6.64 µmol/cm(2).h) and the butyryl esters (6.87 µmol/cm(2).h) had the highest transdermal flux using the Pheroid™ (0.75 - 6.87 µmol/cm(2).h) system.

Artemisinin-quinoline hybrid-dimers: synthesis and in vitro antiplasmodial activity.

Novel artemisinin-quinoline hybrid-dimers were synthesized from dihydroartemisinin and different aminoquinolines at elevated temperatures (90-110°C). All compounds were obtained as the ß-isomers and were tested against both chloroquine sensitive and resistant strains of Plasmodium falciparum. Hybrid-dimer 8 showed the highest antiplasmodial activity, inheriting the optimum chain length of three carbon atoms.

In-vitro transdermal penetration of cytarabine and its N4-alkylamide derivatives.

OBJECTIVES: The aim of this study was to synthesise and determine the transdermal penetration of cytarabine alkylamide derivatives and assess the correlation of flux with physicochemical properties. METHODS: The alkylamide derivatives of cytarabine were synthesised by acylation at the N4-amino group by the mixed anhydride method. The in-vitro permeation studies were performed using the Franz diffusion cell methodology. Furthermore, partition coefficients (n-octanol-water) and aqueous solubility of the N4-alkylamide derivatives of cytarabine were determined in order to obtain information about their lipophilicity and hydrophilicity. KEY FINDINGS: The N4-alkylamides of cytarabine (acetyl, butanoyl, hexanoyl, octanoyl, and decanoyl derivatives) showed decreased hydrophilicity and increased lipophilicity. The log D values of the alkylamides were higher than that of the parent compound and increased linearly as the alkyl chain lengthened. N4-hexanoyl-4-amino-1-[(2R,3S,4R,5R)-3,4-dihydroxy-5-(hydroxymethyl)oxolan-2-yl] pyrimidin-2-one) showed the highest median steady-state flux (J(ss)) of 89.0 nmol/cm(2) per h in the series, which shows a high statistical difference with the parent compound flux value (3.70 nmol/cm(2) per h). CONCLUSIONS: The prodrug approach appears to be a promising strategy for the enhancement of transdermal penetration of cytarabine.

Synthesis and transdermal permeation of novel N4-methoxypoly(ethylene glycol) carbamates of cytarabine.

BACKGROUND: Cytarabine is a deoxycytidine analogue commonly used in the treatment of hematological malignant diseases. Its clinical utility, however, is severely limited by its short plasma half-life because of the catabolic action of nucleoside deaminases. METHOD: In this study, N(4)-carbamate derivatives of cytarabine (1) were synthesized and evaluated for transdermal penetration because this mode of administration may circumvent its limitations. The synthesis of these compounds was achieved in a two-step process. First, the methoxypoly(ethylene glycol) was activated by p-nitrophenyl chloroformate. Second, the activated intermediates were reacted with cytarabine in the presence of N-hydroxysuccinamide to give the N(4)-methoxypoly(ethylene glycol) carbamate derivatives. The transdermal flux values of the N(4)-carbamates of cytarabine were determined in vitro by Franz diffusion cell methodology. Aqueous solubility and log D (pH 7.4) values were determined and assessed for correlation with transdermal flux values. RESULTS: The synthesized carbamates, particularly, (9)-(13), showed increased solubility in both aqueous and lipid media. Log D values decreased as the oxyethylene chain lengthened. CONCLUSION: Although none of the derivatives showed significantly higher transdermal penetration than cytarabine (1), it should be mentioned that the mean for cytarabine N(4)-methoxyethyleneoxycarbamate (8) was 10 times higher and the median was 2 times higher.

Transdermal penetration of cytarabine and its 5'-O alkyl ester derivatives.

The purpose of this study was to synthesize and determine the in vitro transdermal penetration of cytarabine and its 5'-alkyl esters and to establish a correlation, if any, with selected physicochemical properties. The n-alkyl esters were synthesized by acylation of cytarabine (1) at its pharmacophoric 5'-OH. The transdermal flux values of (1) and its esters were determined in vitro using Franz diffusion cell methodology. Aqueous solubility and log D (pH 7.4) values were determined and assessed for correlation to transdermal flux. An inverse relation was observed between the water solubility (Sw) and log D values. Of all esters, (4) exhibited the highest flux value of 22.2 nmol x cm(-2) x h(-1), which is significantly different to that of the parent drug cytarabine (3.70 nmol x cm(-)2 x h(-1)). No trend was found between water solubility and flux values.

Synthesis and in vitro transdermal penetration of methoxypoly(ethylene glycol) carbonate and carbamate derivatives of lamivudine (3TC).

The objective of this study was to determine the in vitro transdermal permeation through the human stratum corneum (SC) of the antiretroviral (ARV) drug lamivudine (3TC) (1) and its synthesised methoxypoly(ethylene glycol) (MPEG) carbamates and carbonates in phosphate buffer solution and with the use of Pheroid as delivery system and to establish a relationship, if any, with selected physicochemical properties. The synthesis and in vitro human skin permeation flux of three N4-methoxypoly(ethylene glycol) carbamates (3)-(5) and three 6'-O-methoxypoly(ethylene glycol) carbonates (6)-(8) of lamivudine are reported. The derivatives were synthesised in a two-step process by coupling activated MPEG oligomers of various chain lengths to either the 4-amino or 6'-hydroxy group of lamivudine. Irrespective of the oligomeric series of derivatives (carbamate or carbonate), the aqueous solubility increases as the MPEG chain lengthens while the solubility in octanol (lipophilicity) remained almost constant. Regardless of the mechanism of diffusion viz. passive (in PBS) or use of enhancer (Pheroid), no derivative penetrate the skin better than the parent drug itself. The use of Pheroid even appeared to significantly retard the skin permeation.

1-Bromo-2-(10ß-dihydro-artemisin-oxy)ethane.

The title compound, C(17)H(27)BrO(5), DEB, is a derivative of artemisinin which is used in malara therapy. The OR-group at C12 is cis to the CH(3)-group at C11 and axially oriented on ring D which has a chair conformation. The crystal packing is stabilized by several weak inter-molecular C-H⋯O inter-actions, which combine to form a C-H-O bonded network parallel to (001).

Synthesis and in vitro transdermal penetration of methoxypoly(ethylene glycol) carbonate derivatives of stavudine.

The objective of this study was to synthesize derivatives of the anti-HIV drug stavudine (d4T) with more favourable physicochemical properties for transdermal delivery in an effort to increase transdermal penetration of stavudine and thus reduce the severe side effects associated with the dose-dependent oral therapy. The synthesis, hydrolytic stability, and in vitro human skin permeation flux of a series of novel methoxypoly(ethylene glycol) (MPEG) carbonates of stavudine are reported. The carbonates were synthesized in a two-step process by coupling the MPEG promoiety of various chain lengths to C-5' of d4T. In kinetic studies the carbonates proved to be markedly stable in weakly acidic phosphate medium (pH 5.0) with half-lives ranging from 16 to 58 days. The aqueous solubility increased as the ethylene oxide chain lengthened. However, there was no significant increase in the estimated solubility in octanol. In vitro in the phosphate buffer (200 mM; pH 5.0) almost all carbonates permeate the human skin. However, the most effective penetrant, the derivative with 3 ethylene oxide units in the side chain, exhibited a flux of 26.1 nmol/cm(2)/h as compared to 59.15 nmol/cm(2)/h of the parent drug stavudine. Thus, no permeation enhancement was observed during this study.

Synthesis of methoxypoly(ethylene glycol) carbonate prodrugs of zidovudine and penetration through human skin in vitro.

OBJECTIVES: The aim of this study was to synthesise a series of novel methoxypoly(ethylene glycol) carbonate prodrugs of the antiretroviral drug zidovudine (azidothymidine, AZT) in an attempt to enhance the physicochemical properties for transdermal delivery, which may reduce the severe side-effects and toxicity associated with high oral doses of AZT. METHODS: Methoxypoly(ethylene glycol) carbonates of AZT were synthesised in two steps: activation of the relevant methoxypoly(ethylene glycol) with p-nitrophenyl chloroformate, followed by reaction with AZT. Analysis of the hydrolytic stability in phosphate buffer at pH 5.0 and 7.4 revealed that all the carbonates were markedly more stable at pH 5.0 than at pH 7.4 (0.01 M), with half-lives ranging from 15 to 44 days at pH 5.0 and from 6 to 24 days at pH 7.4. The potential of the series to penetrate the skin was evaluated in vitro by measuring diffusion through excised abdominal female human skin at pH 5.0. KEY FINDINGS: Prodrugs with 1-3 or 8 oxyethylene units in the methoxypoly(ethylene glycol) moiety were found to permeate the skin whereas those with 12 or 17 units did not. The prodrug with eight oxyethylene units was the most effective penetrant, permeating the skin with a mean flux of 53.3 +/- 46.5 nmol/cm2 per h, which is 2.4-10.1 times that of AZT (8.55 +/- 5.3 nmol/cm2 per h). CONCLUSIONS: The bioreversible conjugation of the methoxypoly(ethylene glycol) promoiety to AZT appears to be a promising strategy for the transdermal delivery of AZT at a therapeutic dose.

N,N-Bis(trifluoromethylquinolin-4-yl)diamino alkanes: synthesis and antimalarial activity.

A series of N,N-bis(trifluoromethylquinolin-4-yl)- and N,N-bis[2,8-bis(trifluoromethyl)quinolin-4-yl] diamino alkane and piperazine derivatives were synthesised by employing a simple and rapid displacement reaction of the 4-chloro group on the 2-trifluoromethyl- and 2,8-bis(trifluoromethyl)-quinoline by diaminoalkane or piperazine groups. Results of in vitro antimalarial activity evaluations of these compounds against the chloroquine-sensitive (D10) and chloroquine-resistant (K1) strains of Plasmodium falciparum indicate that compounds with trifluoromethyl groups in both the 2 and 8 positions coupled with diaminoalkyl bridging chains of 2 to 6 carbon atoms exhibit a slightly higher activity than compound with only a trifluoromethyl group at position 2, and those with a piperazine bridge. These compounds exhibit higher activity in the chloroquine-resistant than in the chloroquine-sensitive strains of the Plasmodium. Comparative studies indicate that the compounds are more selective in their cytotoxicity against the parasite cells. Except for compounds containing a piperazine bridge, this new series of compounds interact with ferriprotoporphyrin IX to more or less the same extent.