The chemical composition of volatile fractions from leaves, flowers and peels of Citrus aurantium growing in Tunisia obtained by hydrodistillation were analysed using GC and GC-MS. Furthermore, the isolated essential oils were evaluated for their in vitro antimicrobial activity against eight bacteria, eight phytopathogenic and nine human pathogenic fungi. The essential oils from peels and its main compound limonene have been found to possess strong contact toxicity against four storage-grain insects. The highest mortality rate was observed when the essential oil was applied against Cryptolestes ferrugineus, Liposcelis bostrychophila and Tribolium castaneum.

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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 1 H NMR, 13 C 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).