Acetylcholinesterase inhibition, antioxidant and cytotoxic activities of Hedychium gardnerianum leaf essential oils from S. Miguel Island were determined. All the oils inhibited acetylcholinesterase, with IC 50 values of approximately 1 mg/mL, showing no statistical differences between collection sites. Three oils presented mixed inhibition, whilst one was almost truly competitive. This activity can be attributed to the presence of sesquiterpenes, which constituted more than 60% of the composition of the oils. Regarding the antioxidant activity as measured by the DPPH method, all the oils presented activities similar to reference compounds, although with statistical differences between collection sites. Cytotoxicity measured using Artemia salina classified these oils as moderately toxic, with LC 50 values ranging from 300 to 500 µg/mL. These results indicate a possible application of these oils in aromatherapy as coadjuvants in the treatment of cognitive diseases such as Alzheimer, since they may contribute to increase acetylcholine in cholinergic neurons and simultaneously fight deleterious oxidations responsible by neurological degeneration.
We report an efficient methodology for the direct oxidative esterification of primary alcohols to diether-esters using pyridinium chlorochromate (PCC). Numerous studies were carried out to probe the reaction mechanism and at the same time optimize the reaction conditions. The reaction could be conducted with 1 equivalent of PCC and 1 equivalent of BF3.OEt2. Indications based on literature precident were that the reaction may proceed via a sequential alcohol oxidation to the aldehyde followed by a putative Cr catalyzed or Boron Claisen-Tishchenko-type reaction. Using this efficient methodology, we synthesized a family of novel diether-esters in very good yields; some of these molecules were subsequently tested against both acetylcholinesterase (AChE) and butyrlcholinesterase (BuChE). In addition, we also disclose a new synthetic strategy for the synthesis of lactam macrocycles with potential biological activity. This methodology included the regioselective borylation of the ester substrate and a subsequent Suzuki-Miyaura coupling to obtain the desired lactam macrocycle.
Many benzofused cyclic chiral alcohols are biologically active and a variety of synthetic methods has been developed to access these structures. Palladium-catalyzed intramolecular nucleophilic addition reactions of aryl boron and aryl halide compounds to carbonyls are useful, but control over the cyclization to give a single product has to-date proven challenging. Here, we describe the first controlled intramolecu-lar nucleophilic addition of aryl bromides to aldehydes, providing the corresponding cycloalkanol or cyclic ketone derivatives simply by changing the base or the ligand. Ten new 3,3-dimethylchroman-4-ol derivatives and six new 3,3-dimethylchroman-4-ones were prepared (with up to 91% conversion and 46% ee).
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