The architecture and bioactivity of natural products frequently serves as an embarkation point for exploration of biologically-relevant chemical space. Total synthesis followed by derivative synthesis has historically enabled a deeper understanding of structure-activity relationships. However, synthetic strategies toward a natural product are not always guided by hypotheses regarding structural features required for bioactivity. Here we report an approach to natural product total synthesis that we term ‘pharmacophore-directed retrosynthesis’. A hypothesized, pharmacophore of a natural product is selected as an early synthetic target and this dictates the retrosynthetic analysis. In an ideal application, sequential increases in structural complexity of this minimal structure enables development of an SAR profile throughout the course of the total synthesis effort. This approach enables the identification of simpler congeners retaining bioactivity at a much earlier stage of a synthetic effort as demonstrated herein for the spongiane diterpenoid, gracilin A, leading to simplified derivatives with potent neuroprotective and immunosuppressive activity.

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The macrolide caniferolide A was isolated from extracts of a culture of the marine-derived actinomycete Streptomyces caniferus, and its ability to ameliorate Alzheimer’s disease (AD) hallmarks was determined. The compound reduced neuroinflammatory markers in BV2 microglial cells activated with lipopolysaccharide (LPS), being able to block NFκB-p65 translocation to the nucleus and to activate the Nrf2 pathway. It also produced a decrease in pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), reactive oxygen species (ROS) and nitric oxide release and inhibited iNOS, JNK, and p38 activities. Moreover, the compound blocked BACE1 activity and attenuated Aβ-activation of microglia by drastically diminishing ROS levels. The phosphorylated state of the tau protein was evaluated in SH-SY5Y tau441 cells. Caniferolide A reduced Thr212 and Ser214 phosphorylation by targeting p38 and JNK MAPK kinases. On the other side, the antioxidant properties of the macrolide were determined in an oxidative stress model with SH-SY5Y cells treated with H2O2. The compound diminished ROS levels and increased cell viability and GSH content by activating the nuclear factor Nrf2. Finally, the neuroprotective ability of the compound was confirmed in two trans-well coculture systems with activated BV2 cells (both with LPS and Aβ) and wild type and transfected SH-SY5Y cells. The addition of caniferolide A to microglial cells produced a significant increase in the survival of neuroblastoma in both cases. These results indicate that the compound is able to target many pathological markers of AD, suggesting that caniferolide A could be an interesting drug lead for a polypharmacological approach to the illness.

Laxaphycins are a family of non-ribosomal lipopeptides that have been isolated from several cyanobacteria. Some of these compounds have presented cytotoxic activities, but their mechanism of action is poorly understood. In this work, the already described laxaphycins B and B3, and acyclolaxaphycins B and B3 were isolated from the marine cyanobacteria Anabaena torulosa. Moreover, two new acyclic compounds, [des-(Ala4-Hle5)] acyclolaxaphycins B and B3, were purified from the herviborous gastropod Stylocheilus striatus, with this being the first description of biotransformed laxaphycins. The structure of these new compounds was elucidated, together with the absolute configuration of acyclolaxaphycins B and B3. The bioactivities of the six peptides were determined in SH-SY5Y human neuroblastoma cells. Laxaphycins B and B3 were cytotoxic (IC50: 1.8 and 0.8 µM, respectively) through the induction of apoptosis. In comparison, acyclic laxaphycins did not show cytotoxicity but affected mitochondrial functioning, so their effect on autophagy-related protein expression was analyzed, finding that acyclic peptides affected this process by increasing AMPK phosphorylation and inhibiting mTOR. This work confirms the pro-apoptotic properties of cyclic laxaphycins B and is the first report indicating the effects on autophagy of their acyclic analogs. Moreover, gastropod-derived compounds presented ring opening and amino-acids deletion, a biotransformation that had not been previously described.

Cyclophilins (Cyps) are ubiquitous proteins that belong to the immunophilins family consistently associated with inflammatory and cardiovascular diseases. While levels of CypA have been extensively studied, less data are available for other Cyps. The purpose of this case-control study was to determine the relationship of Cyps (A, B, C and D) with coronary artery disease (CAD) and eight inflammation markers. Serum levels of Cyps, interleukins and metalloproteinases were measured in serum collected from 84 subjects. Participants were divided into two sub-groups based on CAD diagnosis: 40 CAD patients and 44 control volunteers. Serum levels of CypA, CypB and CypC, IL-1β and IL-6 were significantly higher in CAD patients. Bivariate correlation analysis revealed a significant positive correlation between Cyps and several blood and biochemical parameters. When the ability of Cyps levels for CAD diagnosis was evaluated, higher sensitivity and selectivity values were obtained with CypC (c-statistic 0.891, p < 0.001) indicating that it is a good marker of CAD disease, while less conclusive results were obtained with CypA (c-statistic 0.748, p < 0.001) and CypB (c-statistic 0.655, p < 0.014). In addition, significant correlations of traditional CAD risk factors and CypC were observed. In summary, high levels of CypC are a risk factor for CAD and therefore it can be proposed as a new biomarker for this disease.

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The structures of three new cyclic depsipeptides, tiahuramides A (1), B (2), and C (3), from a French Polynesian collection of the marine cyanobacterium Lyngbya majuscula are described. The planar structures of these compounds were established by a combination of mass spectrometry and 1D and 2D NMR experiments. Absolute configurations of natural and nonproteinogenic amino acids were determined through a combination of acid hydrolysis, derivitization with Marfey's reagent, and HPLC. The absolute configuration of hydroxy acids was confirmed by Mosher's method. The antibacterial activities of tiahuramides against three marine bacteria were evaluated. Compound 3 was the most active compound of the series, with an MIC of 6.7 μM on one of the three tested bacteria. The three peptides inhibit the first cell division of sea urchin fertilized eggs with IC values in the range from 3.9 to 11 μM. Tiahuramide B (2), the most potent compound, causes cellular alteration characteristics of apoptotic cells, blebbing, DNA condensation, and fragmentation, already at the first egg cleavage. The cytotoxic activity of compounds 1-3 was tested in SH-SY5Y human neuroblastoma cells. Compounds 2 and 3 showed an IC of 14 and 6.0 μM, respectively, whereas compound 1 displayed no toxicity in this cell line at 100 μM. To determine the type of cell death induced by tiahuramide C (3), SH-SY5Y cells were costained with annexin V-FITC and propidium iodide and analyzed by flow cytometry. The double staining indicated that the cytotoxicity of compound 3 in this cell line is produced by necrosis.

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