Leishmanicidal activity of aliphatic and aromatic lactones: correlation structure-activity

Antileishmanial activity and immunomodulatory effect of secosubamolide, a butanolide isolated from Nectandra oppositifolia (Lauraceae)

Background:

Visceral leishmaniasis is a complex neglected tropical disease caused by Leishmania donovani complex. Its current treatment reveals strong limitations, especially high toxicity. In this context, natural products are important sources of new drug alternatives for VL therapy. Therefore, the antileishmanial and immunomodulatory activity of compounds isolated from Nectandra oppositifolia (Lauraceae) was investigated herein.

Methods:

The n-hexane extract from twigs of N. oppositifolia were subjected to HPLC/HRESIMS and bioactivity-guided fractionation to afford compounds 1 and 2 which were evaluated in vitro against Leishmania (L.) infantum chagasi and NCTC cells.

Results:

The n-hexane extract displayed activity against L. (L.) infantum chagasi and afforded isolinderanolide E (1) and secosubamolide A (2), which were effective against L. (L.) infantum chagasi promastigotes, with IC₅₀ values of 57.9 and 24.9 µM, respectively. Compound 2 was effective against amastigotes (IC₅₀ = 10.5 µM) and displayed moderate mammalian cytotoxicity (CC₅₀ = 42 µM). The immunomodulatory studies of compound 2 suggested an anti-inflammatory activity, with suppression of IL-6, IL-10, TNF with lack of nitric oxide.

Conclusion:

This study showed the antileishmanial activity of compounds 1 and 2 isolated from N. oppositifolia. Furthermore, compound 2 demonstrated an antileishmanial activity towards amastigotes associated to an immunomodulatory effect.

Oxidation of terminal diols using an oxoammonium salt: a systematic study

A systematic study of the oxidation of a range of terminal diols is reported, employing the oxoammonium salt 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (4-NHAc-TEMPO⁺ BF₄^-) as the oxidant. For substrates bearing a hydrocarbon chain of seven carbon atoms or more, the sole product is the dialdehyde. A series of post-oxidation reactions have been performed showing that the product mixture resulting from the oxidation step can be taken on directly to a subsequent transformation. For diols containing four to six carbon atoms, the lactone product is the major product upon oxidation. In the case of 1,2-ethanediol and 1,3-propanediol, when using a 1 : 0.5 stoichiometric ratio of substrate to oxidant, the corresponding monoaldehyde is formed which reacts rapidly with further diol to yield the acetal product. This is of particular synthetic value given both the difficulty of their preparation using other approaches and also their potential application in further reaction chemistry.

Leishmanicidal Activity and Structure-Activity Relationships of Essential Oil Constituents

Several constituents of essential oils have been shown to be active against pathogens such as bacteria, fungi, and protozoa. This study demonstrated the in vitro action of ten compounds present in essential oils against Leishmania amazonensis promastigotes. With the exception of p-cymene, all evaluated compounds presented leishmanicidal activity, exhibiting IC₅₀ between 25.4 and 568.1 μg mL⁻¹. Compounds with the best leishmanicidal activity presented a phenolic moiety (IC₅₀ between 25.4 and 82.9 μg mL⁻¹). Alicyclic alcohols ((−)-menthol and isoborneol) and ketones ((−)-carvone) promoted similar activity against the parasite (IC₅₀ between 190.2 and 198.9 μg mL⁻¹). Most of the compounds showed low cytotoxicity in L929 fibroblasts. Analysis of the structure-activity relationship of these compounds showed the importance of the phenolic structure for the biological action against the promastigote forms of the parasite.

Phase-Transfer Catalyzed O-Silyl Ether Deprotection Mediated by a Cyclopropenium Cation

The use of a cyclopropenium cation as a phase-transfer catalyst for O-silyl ether deprotection is reported. Mechanistic insight into this deprotection methodology derived by linear free-energy relationships (LFER), quantum theory of atoms in molecules (QTAIM), and density functional theory (DFT) calculations are also provided.