Synthesis, DFT And Antimicrobial Activity Assays Of Novel Cis/Trans-But-2-Enedioic Acid Esters Containing A Hydroxybenzoic Acid Methyl Ester Moiety

Fumarate esters are industrially important substances and widely used in the food andpharmaceutical industries. These compounds with an α, β-unsaturated carbonyl moiety areparticularly reactive, due to the double bond conjugated with the carbonyl group, and havethe capacity to react with nucleophilic groups on peptides, proteins, or DNA by Michaeladdition. However, traditional food preservatives, such as monomethyl fumarate, dimethylfumarate and monoethyl fumarate, cause negative impact on human health, thereby limitingits application in the food industry. To decrease its stimulation, the active structures ofcis/trans-but-2-enedioic acid monoesters and hydroxybenzoic acid methyl ester werecombined to synthesize novel cis/trans-but-2-enedioic acid esters containing ahydroxybenzoic acid methyl ester moiety to discover new bioactive molecules as potentialfood preservatives against fungi and bacteria.In this paper, compounds (3-6c) were synthesized from maleic anhydride andhydroxybenzoic acid methyl ester through maleic acid mono-esterification, cis/transisomerization and acyl chloride estification.1. Synthesis of cis-but-2-enedioic acid monoesters (1a-c): cis-but-2-enedioic acidmonoesters were synthesized from maleic anhydride, anhydrous Na2CO3and monohydricalcohol (methanol, ethanol and propanol) through salt forming reaction and acidification.2. Cis/trans isomerization: trans-but-2-enedioic acid monoesters (2a-c) were preparedin the presence of catalyst (anhydrous AlCl3) by isomerization of the correspondingmonoalkyl maleates. The effects of reaction temperature, time and catalyst dosage on theyield of product were investigated. Under the optimum conditions, the yield of monomethylfumarate (2a), monoethyl fumarate (2b) and monopropyl fumarate (2c) was84.5%,54%and35.5%, respectively.3. Acyl chloride estification: with the cis/trans-but-2-enedioic acid monoesters andhydroxybenzoic acid methyl ester as starting materials, NaH as acid binding agent,cis/trans-but-2-enedioic acid esters containing a hydroxybenzoic acid methyl ester moiety(3-6c) were synthesized by the acyl chloride estification.4. All the prepared compounds were analyzed by melting point, HPLC, LC-MS,1HNMR and13C NMR.4-(methoxycarbonyl) phenyl ethyl fumarate (6b) was alsocharacterized by single-crystal X-ray diffraction.The antibacterial and antifungal activities in vitro of these compounds against S.choleraesuis subsp. choleraesuis, B. subtilis, L. lactis subsp. lactis, C. albicans, S. cerevisiae, A. flavus, A. niger and P. chrysogenum were studied. The results showed that theantibacterial and antifungal activities of the newly synthesized compounds were strongerthan that of the single monomethyl fumarate and methyl4-hydroxybenzoate. Most of thenewly synthesized compounds were effective against bacteria and fungi within200μg/mL.Among the antibacterial and antifungal compounds,4-(methoxycarbonyl) phenyl methylfumarate (6a) showed the best antimicrobial activity, compound6a was effective against S.choleraesuis subsp. choleraesuis, B. subtilis, L. lactis subsp. lactis, C. albicans, S.cerevisiae, A. flavus, A. niger and P. chrysogenum within50、50、50、25、25、37.5、75and37.5μg/mL, respectively. The microbiocidal activity of compound6a gainst S. choleraesuissubsp. choleraesuis, L. lactis subsp. lactis and S. cerevisiae was confirmed by time–kill, andit was found that the log values for the pathogens were significantly reduced by compound6a at1.5MIC.The electronic properties of these compounds (3-6c) were calculated by the densityfunctional theory (DFT) method with6-31G (d, p) basis set. DFT studies indicated thatmolecular electrostatic potential (MEP) map, ELUMO, energy gap, electronegativity andelectrophilicity index could be helpful to understand the various antimicrobial activitiesamong these compounds. The results of SAR analysis indicated that the antimicrobialactivity of cis/trans-but-2-enedioic acid esters containing a hydroxybenzoic acid methylester moiety (3-6c) increased with decreasing values of ELUMO. Furthermore, isomers (3-6a)with high chemical reactivity had strong antibacterial and antifungal activity. Homologouscompounds (6a-6c) with low dipole moment had strong antibacterial and antifungal activity.