Compounds for treating preventing malaria and, particularly, to larvicidal agents that are 4-[(substituted 1H-benzimidazol-2-ylsulfanyl)methyl]-6-substituted-2H-chromen-2-ones derivatives and their use as larvicidal agents.

BACKGROUND

The present disclosure relates to synthesis of 4-[(substituted 1H-benzimidazol-2-ylsulfanyl)methyl]-6-substituted-2H-chromen-2-ones and their use as larvicidal agent.

2. Description of the Related Art

Malaria is considered one of the most challenging life-threatening diseases initiated by parasites that are transmitted to humans through the bites of infectedAnophelesmosquitoes. It affects both genders, leading to severe health impacts and negative socioeconomic impacts. Recently, the World Health Organization (WHO) reported that there were an estimated 228 million cases of malaria spanning 87 countries. TheAnopheles arabiensismosquito is considered one of the major vectors of malaria. The path of infection starts with a bite from an infected female mosquito, where the parasite is delivered into circulatory system and ultimately to the liver where it become mature and reproduces.

There are many approaches and strategies for the management of Malaria. One of the most effective strategies is to eliminate the vector through environmental modifications and biological control, The use of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) or safe synthetic larvicidal agents are candidates for biological control. Since insecticide resistance threatens the management of vectors, it is necessary to prioritize development of potent new biological active compounds as well as to aid in resistance management.

Thus, new insecticides and/or pesticides solving the aforementioned problems are desired.

SUMMARY

In the process of designing and developing a novel larvicidal agent, a series of 4-[(substituted 1H-benzimidazol-2-ylsulfanyl)methyl]-6-substituted-2H-chromen-2-ones derivatives have been developed by a one-step synthetic chemical method. The present subject matter relates to the synthesis of an anti-malarial drug designed to kill, for example, the mosquito vectorAnopheles arabiensisat the larval stage. The compounds were evaluated for larvicidal activity, for example againstAnopheles arabiensis, by standard WHO larvicidal protocols. Tested compounds resulted in high overall larval mortality of greater than 70% after 24 hours and 48 hours.

In an embodiment, the present subject matter relates to a compound having the formula I.

wherein:R1is selected from the group consisting of CH3and C(CH3)3; andR2is selected from the group consisting of an optionally substituted benzimidazole, an optionally substituted benzoxazole, an optionally substituted benzothiazole, and an optionally substituted thiadiazole. In various embodiments, the benzimidazole may be substituted with a methoxy group. In other embodiments, the thiadiazole may be substituted with a methyl group.

In one embodiment, the present subject matter relates to a method of killing insects and larva, the method comprising applying to the food of said insects and larva in a target site of insect infestation a larvicidal effective amount of the larvicidal active composition the formula I.

wherein:R1is selected from the group consisting of CH3and C(CH3)3; andR2is selected from the group consisting of an optionally substituted benzimidazole, an optionally substituted benzoxazole, an optionally substituted benzothiazole, and an optionally substituted thiadiazole.

In various embodiments, the benzimidazole may be substituted with a methoxy group. In other embodiments, the thiadiazole may be substituted with a methyl group.

In another embodiment, the present subject matter relates to the use of an insecticidally acceptable composition comprising an insecticidally effective amount of the compounds of formula I, including a number of species or specific structures falling under structural formula I.

In a further embodiment, the present subject matter relates to a method of killing insects comprising applying to food of the insects or to a target site of insect infestation an insecticidally effective amount of compounds of formula I.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Definitions

As used herein, “alkyl” refers to a straight-chain or branched saturated hydrocarbon group. Examples of alkyl groups include methyl (Me), ethyl (Et), propyl (e.g., n-propyl and z′-propyl), butyl (e.g., n-butyl, z′-butyl, sec-butyl, tert-butyl), pentyl groups (e.g., n-pentyl, z′-pentyl, -pentyl), hexyl groups, and the like. In various embodiments, an alkyl group can have 1 to 40 carbon atoms (i.e., C1-C40alkyl group), for example, 1-30 carbon atoms (i.e., C1-C30alkyl group). In some embodiments, an alkyl group can have 1 to 6 carbon atoms, and can be referred to as a “lower alkyl group” or a “C1-C6alkyl group”. Examples of lower alkyl groups include methyl, ethyl, propyl (e.g., n-propyl and z′-propyl), and butyl groups (e.g., n-butyl, z′-butyl, sec-butyl, tert-butyl). In some embodiments, alkyl groups can be substituted as described herein. An alkyl group is generally not substituted with another alkyl group, an alkenyl group, or an alkynyl group.

The term “substituted alkyl” as used herein refers to an alkyl group in which 1 or more (up to about 5, for example about 3) hydrogen atoms is replaced by a substituent independently selected from the group: —O, —S, acyl, acyloxy, optionally substituted alkoxy, optionally substituted amino (wherein the amino group may be a cyclic amine), azido, carboxyl, (optionally substituted alkoxy)carbonyl, amido, cyano, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, halogen, hydroxyl, nitro, sulfamoyl, sulfanyl, sulfinyl, sulfonyl, and sulfonic acid. Some of the optional substituents for alkyl are hydroxy, halogen exemplified by chloro and bromo, acyl exemplified by methylcarbonyl; alkoxy, and heterocyclyl exemplified by morpholino and piperidino. Other alkyl substituents as described herein may further be contemplated.

It will be understood by those skilled in the art with respect to any chemical group containing one or more substituents that such groups are not intended to introduce any substitution or substitution patterns that are sterically impractical and/or physically non-feasible.

The term “isomers” or “stereoisomers” as used herein relates to compounds that have identical molecular formulae but that differ in the arrangement of their atoms in space. Stereoisomers that are not mirror images of one another are termed “diastereoisomers” and stereoisomers that are non-superimposable mirror images are termed “enantiomers,” or sometimes optical isomers. A carbon atom bonded to four non-identical substituents is termed a “chiral center.” Certain compounds herein have one or more chiral centers and therefore may exist as either individual stereoisomers or as a mixture of stereoisomers. Configurations of stereoisomers that owe their existence to hindered rotation about double bonds are differentiated by their prefixes cis and trans (or Z and E), which indicate that the groups are on the same side (cis or Z) or on opposite sides (trans or E) of the double bond in the molecule according to the Cahn-Ingold-Prelog rules. All possible stereoisomers are contemplated herein as individual stereoisomers or as a mixture of stereoisomers.

The present subject matter relates to the synthesis of an anti-malarial drug designed to kill, for example, the mosquito vectorAnopheles arabiensisat the larval stage. The compounds were evaluated for larvicidal activity, for example againstAnopheles arabiensis, by standard WHO larvicidal protocols. Tested compounds resulted in high overall larval mortality of greater than 70% after 24 hours and 48 hours.

In an embodiment, the present subject matter relates to a compound having the formula I.

wherein:R1is selected from the group consisting of: CH3and C(CH3)3; andR2is selected from the group consisting of an optionally substituted benzimidazole, an optionally substituted benzoxazole, an optionally substituted benzothiazole, and an optionally substituted thiadiazole. In various embodiments, the benzimidazole may be substituted with a methoxy group. In other embodiments, the thiadiazole may be substituted with a methyl group.

In one embodiment, where R1is CH3, R2may be selected from the group consisting of 1H-benzimidazole, 6-methoxy-1H-benzimidazole, 1,3-benzoxazole, 1,3-benzothiazole, and 5-methyl-1,3,4-thiadiazole. Similarly, where R1is C(CH3)3, R2may be selected from the group consisting of 1H-benzimidazole, 6-methoxy-1H-benzimidazole, 1,3-benzoxazole, 1,3-benzothiazole, and 5-methyl-1,3,4-thiadiazole.

Said differently, the present subject matter can related to compounds of formula I, i.e. 4-[(substituted 1H-benzimidazol-2-ylsulfanyl)methyl]-6-substituted-2H-chromen-2-ones, selected from the group consisting of:

It is to be understood that the present subject matter covers all combinations of substituent groups referred to herein.

In additional embodiments, the compound of formula I is considered as larvicidal agent. Accordingly, the present compound is capable of killing the larval stage of an insect.

In another embodiment, the present subject matter relates to an insecticidally acceptable composition comprising an insecticidally effective amount of compound of formula I and an insecticidally acceptable carrier.

In some embodiments, the present compositions and methods of use can be used for combination treatment, where other insecticidal ingredients can be included therein, or can be co-administered therewith.

Non-limiting examples of suitable excipients, carriers, or vehicles useful herein include liquids such as water, saline, glycerol, polyethylene glycol, hyaluronic acid, ethanol, and the like. Suitable excipients for nonliquid formulations are also known to those of skill in the art.

The present compounds are typically administered at an insecticidally effective dosage, e.g., a dosage sufficient to provide a desired activity against insects.

While insecticidal dosage levels have yet to be optimized for the present compounds, generally, each treatment of the present compositions could be expected to include 1 mg/mL in 1 mL of a suitable carrier and 249 mL of water to obtain a final concentration of 4 μg/mL, of the present compounds. The precise effective amount will vary from treatment to treatment and will depend upon the target area of application, the insect species being treated for, the number of insects present, and the like. The treatment area may be administered as many doses as is required to produce an effective treatment.

Liquid compositions can, for example, be prepared by dissolving, dispersing, etc. the active compound as defined above and optional adjuvants in a carrier, such as, for example, water, saline, aqueous dextrose, glycerol, glycols, ethanol, and the like, to thereby form a solution or suspension. If desired, the composition to be administered may also contain minor amounts of nontoxic auxiliary substances such as wetting agents, emulsifying agents, or solubilizing agents, pH buffering agents and the like, for example, sodium acetate, sodium citrate, cyclodextrin derivatives, sorbitan monolaurate, triethanolamine acetate, triethanolamine oleate, etc.

In a further embodiment, the present subject matter relates to a method of killing insects and larva comprising applying to said insects or to a target site of insect infestation an insecticidally effective amount of the compound of formula I and/or a composition containing the same.

In an embodiment, the present methods of killing insects can be effective against insects belonging to a speciesAnopheles arabiensisof mosquitos. Accordingly, the present compounds can be used as an insecticide to control populations of harmful insect pests, including, by way of non-limiting example, cockroaches and fleas.

In another embodiment, in the present methods of killing insects, the compounds as described herein, as exemplified by the 4-[(1,3-benzoxazol-2-ylsulfanyl)methyl]-6-methyl-2H-chromen-2-one (3c) compound, can have a high larval mortality rate of 70.13±2.29 in 24 hours and 75.77±2.21 in 48 hours.

In yet another embodiment, in the present methods of killing insects, the 6-methyl-4-{[(5-methyl-1,3,4-thiadiazol-2-yl)sulfanyl]methyl}-2H-chromen-2-one (3e) compound can have a high larval mortality rate of 77.21±2.02 in 24 hours and 82.19±1.93 in 48 hours.

In still another embodiment, in the present methods of killing insects, the 4-[(1,3-benzothiazol-2-ylsulfanyl)methyl]-6 tert-butyl-2H-chromen-2-one (3i) compound can have a high larval mortality rate of 89.92±2.44 in 24 hours and 94.66±2.11 in 48 hours.

In still another embodiment, in the present methods of killing insects, 4-{[(5-methyl-1,3,4-thiadiazol-2-yl)sulfanyl]methyl}-6 tert-butyl-2H-chromen-2-one (3j) compound can have a high larval mortality rate of 94.72±2.61 in 24 hours and 95.11±2.09 in 48 hours.

In a further embodiment of the present methods, the compounds of formula I can be applied to animal food. More specifically, the compounds of formula I can be applied to cat food. In additional embodiments, the compounds of formula I can be ingested by the larva of the speciesAnopheles arabiensis.

In an embodiment, the present methods of controlling mosquitos can be effective against mosquitos belonging to a speciesAnopheles arabiensis.

In a further embodiment, the present subject matter relates to a method of making 4-[(substituted 1H-benzimidazol-2-ylsulfanyl)methyl]-6-substituted-2H-chromen-2-ones derivatives of compound I, the method comprising: adding a mercapto substituted molecule to a catalytic amount of anhydrous K2CO3in dimethylformamide (DMF) and stirring for at least about half an hour, for about 25 minutes, or for about 35 minutes. Next, substituted 4-(bromomethyl)-2H-chromen-2-one is added to the mixture, and stirring is continued at room temperature for about 10 hours to about 12 hours. Completion of the reaction can be monitored on thin layer chromatography (TLC), and after cooling, the solid obtained is filtered, dried, and recrystallized using ethyl alcohol.

In certain embodiments, about 2 mmol of the mercapto substituted molecule can be used. In other embodiments, about 10 mol % of the anhydrous K2CO3in DMF can be used. In further embodiments, about 2 mmol of the 4-(bromomethyl)-2H-chromen-2-one can be used

The present production methods can be further seen by referring to the following Scheme 1:

The following examples relate to various methods of manufacturing certain specific compounds and application results as described herein. All compound numbers expressed herein are with reference to the synthetic pathway figures shown above.

EXAMPLES

The general process for designing of 4-[(substituted 1H-benzimidazol-2-ylsulfanyl)methyl]-6-substituted-2H-chromen-2-ones derivatives is a one-pot reaction:

General Procedure for the Synthesis of Methylene Thio-Linked Coumarin Derivatives (3a-j)

A mercapto substituted molecule (2 mmol) was added to a catalytic amount of anhydrous K2CO3(10% mol) in DMF and stirred for half an hour. Substituted 4 (bromomethyl)-2H-chromen-2-one (2 mmol) was added to the mixture, and stirring was continued at room temperature for 10 hours to 12 hours. Completion of the reaction was monitored on TLC, and after cooling, the solid obtained was filtered, dried, and recrystallized using ethyl alcohol.

The chemical characteristics of each of the synthesized compounds are illustrated below in Table 1.

Anopheles arabiensiswas used in the study according to the protocol described by WHO (1975) guidelines in an insectary simulating the temperature (27.5° C.), humidity (70%), and lighting (12/12) of a malaria-endemic environment. One mL of test compound (1 mg/mL) was added to 1 mL of acetone and followed by 249 mL of distilled water to obtain a final concentration of 4 μg/mL. Thirty individuals of 3rd instar larvae were introduced into a container. Negative control was set up using the solvent (acetone) and distilled water, and a positive control included Temephos, which is an active emulsified organophosphate larvicidal used by malaria control programs. Larval mortality was examined for each container separately for 24 h and fed specially made cat food that contained less oil/fat content. The percentage of mortality was determined relative to the initial number of larvae exposed.

Statistical Analysis

Differences in larval mortality between treatments were assessed with generalized linear models using a quasi-Poisson link function.Anopheles arabiensismortality was the dependent variable, while fixed effects were test compounds and observation period (24 and 48 h). A p-value <0.05 was considered statistically significant. Throughout the text, the results are presented as the adjusted mean the standard error.

The results of the larvicidal screening can be observed in Table 2, below.

It is to be understood that the methods of making and the 4-[(substituted 1H-benzimidazol-2-ylsulfanyl)methyl]-6-substituted-2H-chromen-2-ones derivatives, and the use of compositions containing the same, are not limited to the specific embodiments described above, but encompasses any and all embodiments within the scope of the generic language of the following claims enabled by the embodiments described herein, or otherwise shown in the drawings or described above in terms sufficient to enable one of ordinary skill in the art to make and use the claimed subject matter.