Novel antimicrobial and anti-acetylcholinesterase dihydroisoxazoles from (R)-limonene

We report herein the convenient procedures for the efficient and easy synthesis, and the antimicrobial and the anti-acetylcholinesterase evaluation of two new series of (R)-limonene derivatives. A substantial modification aimed at targeting to discover novel structures with a better antimicrobial and anti-acetylcholinesterase (anti-AChE) activities. The condensation of (R)-limonene (1) with various arylnitrile oxides led, via the 1,3-dipolar cycloaddition reaction, conducted with complete region-specificity, to a series of new limonene-dihydroisoxazoles, 2a-h. On the other hand, N-alkylation of the previously prepared limonene-lactam derivative (3) yielded the corresponding dipolarophile (4), which affords by condensation with arylnitrile oxides the expected new dihydroisoxazoles, 5a-h. The target compounds were completely characterized by 1H NMR, 13C NMR and MS. All the synthesized heterocyclic compounds were tested for their antimicrobial and anti-acetylcholinesterase activities. The dihydroisoxazoles 2a (IZ = 13.25 mm, cc = 1 mg/mL) and 5b (IZ = 13.75 mm, cc = 1 mg/mL) exhibited the highest antifungal activity. The greatest anti-acetylcolinesterase activity was exhibited by 2f (IC50 = 82±3 µg/mL) and by 5a (IC50 = 99±1 µg/mL)

Semi-synthesis of new antimicrobial esters from the natural oleanolic and maslinic acids

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