Thermodynamics of partitioning of the antimalarial drug mefloquine in phospholipid bilayers and bulk solvents.

The antimalarial drug mefloquine binds avidly to phospholipids in biomembranes. The thermodynamics of the partitioning process in dimyristoylphosphatidylcholine (DMPC) bilayers was investigated to give some insight into the drug-phospholipid interaction. Thermodynamic parameters for the partition equilibria were evaluated from the equilibrium partition coefficients measured as a function of temperature. Negative values of delta H and delta S were obtained for the transfer of mefloquine from the aqueous to the gel phase of the phospholipid. The partitioning is enthalpy controlled which suggests that mefloquine interacts strongly with the phospholipid phase. In contrast, the partitioning of mefloquine into the liquid crystalline phase of DMPC is entropy controlled which is typical of a hydrophobic interaction between mefloquine and the aqueous phase. The partitioning of mefloquine into the bulk solvents octanol and hexane were found to be enthalpy and entropy controlled, respectively. The enthalpy dominated partitioning of mefloquine into gel phase DMPC and octanol is attributed to the occurrence of hydrogen bonding and van der Waals interactions between solute and solvent. The flat shape of mefloquine may further aid its interaction with the orderly domains of the lipidic/organic phase. This is apparent from a comparison of the partitioning characteristics of another structurally related but conformationally different molecule, quinine into DMPC and octanol.

Molecular geometry and physiochemical characteristics of selected anilinoquinolines, indolo[3,2-c]quinolines and tetrahydroindolo[3,2-d]benzazepines.

The molecular geometry, acid dissociation constants and partition coefficients of the anilinoquinoline (I), indolo[3,2-c]quinoline (II) and tetrahydroindolo[3,2-d] [1]benzazepine (III) ring systems have been determined using representative compounds: 7-chloro-4-(p-anisidino)quinoline (Ia), 3-chloro-8-methoxy-11H-indolo[3,2-c]-quinoline (IIa) and 3-chloro-9-methoxy-5,6,7,12-tetrahydroindolo[3,2-d] [1]benzazepine (IIIa). Ring systems II and III are cyclic analogues of I. The minimum energy conformation was determined by molecular mechanics. Compound IIa is the most planar and conformationally restricted, followed by IIIa and Ia. The acid dissociation constants (pKa) were determined by the solubility method. The ring nitrogen of Ia is most basic, followed by that of IIa and IIIa. The partition coefficient (log P) was determined between octanol and appropriate aqueous buffers by the shaken flask method. Hydrophobicity decreases in the order of Ia > IIa > IIIa. Factors contributing to the different molecular geometry, pKa and hydrophobicity of these related compounds are discussed. The present study may contribute to the design of better drugs with ring system I, II or III.

Pharmacological activity and structure-activity relationship of (+/-)-erythro-mefloquine and related compounds on the isolated mouse phrenic nerve diaphragm preparation.

The effects of the antimalarial agent, (+/-)-erythro-mefloquine and related compounds [(+/-)-threo-mefloquine, (+/-)-erythro-N-methylmefloquine and its N-oxide, quinine, WR 184806 and halofanthrine] on the isolated mouse phrenic nerve diaphragm preparation were investigated. Based on their pharmacological effects, these compounds may be divided into two groups. The group I compounds, comprising (+/)-erythro-mefloquine, (+/-)-threo-mefloquine and WR 184806, were found to exert a contractile effect on the muscle and also to inhibit the indirectly (nerve) stimulated and directly (muscle) stimulated (after alpha-bungarotoxin) twitch responses. The group II compounds, comprising the other compounds except halofanthrine, lacked a contractile effect on muscle but potentiated the directly stimulated twitch responses (after alpha-bungarotoxin). Halofanthrine did not elicit any response from the preparation. The minimum energy conformations of these compounds were determined using an interactive molecular modelling program which incorporates MMX force field for molecular mechanics calculations. Conformational analyses of the erythro and threo isomers of mefloquine hydrochloride were also undertaken using 1H-NMR. The 1H-NMR data supported the proposal made on the basis of MMX calculations that the erythro isomer exists in solution as one predominant conformer whereas the threo isomer is present in solution as a mixed population of two stable conformers. The structure-activity relationship of the compounds is discussed.

Improved methods in the synthesis of 1 alpha-hydroxylated vitamin D.

Alternative methods that can be used to synthesize certain key intermediary compounds in the preparation of 1 alpha-hydroxylated vitamin D have been described. These methods are simple and give higher yields than the reported procedures.

Inhibition of acetylcholinesterase by diastereomers of 2-methylamino-1-phenylpropanol and their derivatives.

The anti-acetylcholinesterase activities of the ephedrine diastereomers and their N-methyl derivatives were correlated to the conformation of the molecules in solution. The stereospecificity exhibited by enantiomers of N-methyl-psi-ephedrine was attributed to the predominance of one preferred conformation. The possibility of predicting the absolute configuration of chiral inhibitors from enzyme inhibitions data is discussed.

Long-acting contraceptive agents: levonorgestrel esters of unsaturated acids.

Esters of levonorgestrel (13 beta-ethyl-17 beta-ethynyl-17 beta-hydroxygon-4-en-3-one) with a variety of unsaturated carboxylic acids have been synthesized for evaluation as potential long-acting, injectable contraceptive agents.

PIP: This paper describes the synthesis of esters of levonorgestrel (13 beta-ethyl-17 beta-ethynyl-17 beta-hydroxygon-4-en-3-one) with a variety of unsaturated carboxylic acids for evaluation as potential longacting injectable contraceptive agents. 1-Cyclohexenylacetic acid was prepared by the hydrolysis of 1-cyclohexenylacetonitrile. The synthesis of E-penta-2,4-dienoic acid was achieved by the condensation of acrolein with malonic acid. Reformatsky reaction between crotonaldehyde and ethyl 2-bromopropionate followed by dehydration of the condensation product was used for the synthesis of E,E-2-methylhexa-2,4-dienoic acid. In the preparation of 5-methyl-2-furylacetic acid, 5-methylfurfural was subjected to condensation reaction with rhodanine followed by hydrolysis. The levonorgestrel esters were synthesized by reaction of the appropriate acid chloride with the thallim salt of levonorgestrel, which was obtained by use of thallous ethoxide. The esters prepared were levonorgestrel 1-cyclohexenylacetate; levonorgestrel 1-cyclopentenylacetate; levonorgestrel E-penta-2,4-dienoate; levonorgestrel E,E-2methylhexa-2,4-dienoate; levonorgestrel 5-methyl-2-furylethaoate; levonorgestrel 3-(5'-methyl-2'-furyl)propanoate; levonorgestrel 3-(5'-ethyl-2'-furyl)propanoate; leveonorgestrel 4-(5'-methyl-2'-furyl)butanoate; levonorgestrel E-non-2-en-4-ynoate; 1-cyclohexenylacetic acid; 1-cyclopentenylacetic acid; E-penta-2,4-dienoic acid; E,E-2-methylhexa-2,4-dienoic acid; 5-methyl-2-furylacetic acid; and E-non-2-en-4-ynoic acid.

Long-acting contraceptive agents: norethisterone esters of arylcarboxylic acids.

The synthesis of esters of norethisterone (17 alpha-ethynyl-17 beta-hydroxy-estr-4-en-3-one) with acids containing a benzene ring is described, two methods of esterification being compared in terms of yield and convenience. The activities of these esters as long-acting contraceptive agents have been evaluated.

Long-acting contraceptive agents: furylalkylcarboxylic acid esters of norethisterone.

5-Methyl- and 5-ethyl-furylalkylcarboxylic esters of norethisterone (17 alpha-ethynyl-17 beta-hydroxyestr-4-en-3-one) were prepared in high yield in the presence of thallous ethoxide. The activities of these compounds as long-acting contraceptive agents have been evaluated.

Hydrophobicity and antifilarial activities of 4-aminoquinolines.

The apparent partition coefficients (Papp.) of eight 4-aminoquinolines in 1-octanol/pH 7.4 buffered solutions have been determined and correlated with their reported antifilarial activities. Antifilarial activity appears to be present only in those 4-aminoquinolines which have log Papp. values falling within a narrow range of 2.8 to 3.2.

Synthesis of some novel amodiaquine analogues as potential antimalarial and antifilarial compounds.

Ten amodiaquine analogues, which are hybridized molecules of amodiaquine and diethylcarbamazine, were designed and synthesized. Six analogues, all bearing a basic tertiary amino function at their side chain, were active against Plasmodium berghei in mice and inhibited the mobility of adult worms and microfilariae of Breinlia booliati in vitro. They were inactive against Litomosoides carinii in Mastomys natalensis. The most active antimalarial compound, 7-chloro-4-[alpha-[[N-(4-methyl-1-piperazinyl)carbonyl]amino]-4-hydroxy-m-toluidino]quinoline, had twice the activity of amodiaquine. O-Methylation and N-ethylation generally reduced antimalarial activity. Analogues which lack a basic tertiary amino function at their side chain were also lacking in both antimalarial and antifilarial activities.

Investigation of the anti-acetylcholinesterase activities of the antimalarial agent, amodiaquine, and related compounds.

The antimalarial agent, amodiaquine, is a potent inhibitor of AChE (Ki = 1.50 x 10(-9) M, pH 7.4, 25 degrees C). Both the protonated diethylamino and phenolic hydroxyl functions of amodiaquine are necessary for interaction with AChE. This suggests that the inhibition of AChE by amodiaquine may involve binding of the protonated diethylamino and phenolic hydroxyl functions to the anionic and esteric sites of the enzyme respectively. The anti-AChE property of amodiaquine may be related in some way to the gastrointestinal and central nervous system disturbances frequently encountered when large doses of amodiaquine are used for the treatment of malaria.