NITROGEN ENRICHED CHEMICALLY ENGINEERED EXTRACTS AS SOURCE OF ANTIMYCOBACTERIAL COMPOUNDS

GAGO, GABRIELA; RAMALLO, I AYELEN; GRAMAJO, HUGO; PARES, VIRGINIA; FURLAN, RICARDO

Ouro Preto, Minas Gerais, Brazil

Simposio; Tuberculosis: Science Aimed at Ending the Epidemic; 2020

Keystone

The unremitting success of natural product scaffolds as platforms for drug discovery has increased the interest in the development of strategies for natural product diversification. The chemical engineering of natural extracts is a strategy that points to the transformation of a high proportion of the natural components of crude extracts to produce bioactive semisynthetic compounds. Such change in composition is achieved through chemical treatment with reagents that introduce desired elements and/or produce changes in the molecular squeletons of the natural starting materials. Therefore, the resultant chemically engineered extracts (CEEs) are complex mixtures, enriched in molecules that include both portions from natural origin and elements that are seldom found in natural products.In this work, we present the chemical diversification of a set of 40 essential oils (EOs) with hydroxylamine in refluxing ethanol to produce chemically engineered EOs with different chemical composition, according to the GC-MS/NMR analysis. Then the chemically engineered EOs were studied for Mycobacterium smegmatis growth inhibition properties using a microplate assay at 200 µg/mL final concentration. Of the whole set, the chemically engineered Cuminum cyminum L. essential oil (CCY-M) showed one of the most interesting inhibitory properties against this microorganism. Quantitative biological analysis of CCY-M and the starting essential oil C. cyminum (CCY) was performed giving a MIC= 50 μg/mL and a MIC> 200 μg/mL, respectively. A M. smegmatis TLC-bioautography assay was developed ad hoc, and applied to the CCY-M showing an intense inhibition halo that was absent in CCY. The reaction was scaled up and, the bioassay-guided fractionation of CCY-M led to the purification of one compound that was identified by NMR and HRMS as (Z)-4-isopropyl benzaldehyde oxime (1). This isolated structure contains the N-OH moiety confirming that it is a product of the reaction. This compound was probably generated by the reaction of cuminaldhyde (major constituent of CCY) with hydroxylamine. Interestingly, the oxime 1 MIC was 9.06 µM for M. smegmatis and 72.45µM for M. tuberculosis H37Ra.Future chemical modifications of oxime 1 must be introduced to increase its activity against M. tuberculosis. However, the most relevant point reported here is the potential of the chemical diversification of natural mixtures as a simple and low cost strategy to produce new antimycobacterial molecules.