What is the driving force behind molecular triangles and their guests? A quantum chemical perspective about host-guest interactions.

The physical nature of host-guest (HG) interactions occurring between molecular triangles and linear anions was explored using density functional theory (DFT) calculations combined with energy decomposition analyses (EDA), nuclear independent chemical shift (NICS), and non-covalent interaction index (NCI). We demonstrate that: (i) in addition to the host being significantly rigid, the strain energies are not negligible, especially for host 2; (ii) halogen anions interact mainly by electrostatic forces (ΔEelst > ΔE > ΔEdisp), meanwhile; (iii) trihalogen anions interact mostly by dispersion forces (ΔEdisp > ΔEelst≈ΔE). The NICS and NCI calculations corroborate the idea that HG interactions are considerably mediated through dispersion terms, and also indicate an antiaromatic character inside the host walls.

In vitro cytotoxicity and structure-activity relationship approaches of ent-kaurenoic acid derivatives against human breast carcinoma cell line.

In this study, ent-kaurenoic acid derivatives were obtained by microbial transformation methodologies and tested against breast cancer cell lines (MCF-7). A multivariate quantitative-structure activity relationship (QSAR) analysis was performed taking into account both microbial transformation derivatives and other analogues previously reported in literature to give some insight into the main features behind the cytotoxic activity displayed by kaurane-type diterpenes against MCF-7 cells. The partial least square regression (PLS) method was employed in the training set and the best PLS model was built with a factor describing 69.92% of variance and three descriptors (logP, εHOMO and εHOMO-1) selected by the Ordered Predictors Selection (OPS) algorithm. The QSAR model provided reasonable regression (Q2 = 0.64, R2 = 0.72, SEC = 0.29 and SEV = 0.33). The model was validated by leave-N-out cross-validation, y-randomization and external validation (R2pred = 0.89 and SEP = 0.27). The selected descriptors indicated that the activity was mainly related to electronic parameters (HOMO and HOMO-1 molecular orbital energies), as well as to logP. These findings suggest that higher activity values are directly related with both higher logP and frontier orbital energy values. The positive relationship between these orbitals and the activity suggests that the ent-kaurenoic acid analogues interaction with the target involves charge displacement, which is entirely consistent with the literature. Based on these findings, three compounds were proposed and one of them was synthesized and tested. The experimental result confirmed the activity predicted by the model.

Copaifera duckei Oleoresin and Its Main Nonvolatile Terpenes: In Vitro Schistosomicidal Properties.

In this article, the in vitro schistosomicidal effects of three Brazilian Copaifera oleoresins (C. duckei, C. langsdorffii, and C. reticulata) are reported. From these botanical sources, the oleoresin of C. duckei (OCd) demonstrated to be the most promising, displaying LC50 values of 75.8, 50.6, and 47.2 µg/ml at 24, 48, and 72 h of incubation, respectively, against adult worms of Schistosoma mansoni, with a selectivity index of 10.26. Therefore, the major compounds from OCd were isolated, and the diterpene, (-)-polyalthic acid (PA), showed to be active (LC50 values of 41.7, 36.2, and 33.4 µg/ml, respectively, at 24, 48, and 72 h of incubation). Moreover, OCd and PA affected the production and development of eggs, and OCd modified the functionality of the tegument of S. mansoni. Possible synergistic and/or additive effects of this balsam were also verified when a mixture of the two of its main compounds (PA and ent-labd-8(17)-en-15,18-dioic acid) in the specific proportion of 3:1 (w/w) was tested. The obtained results indicate that PA should be considered for further investigations against S. mansoni, such as, synergistic (combination with praziquantel (PZQ)) and in vivo studies. It also shows that diterpenes are an important class of natural compounds for the investigation of agents capable of fighting the parasite responsible for human schistosomiasis.