Five undescribed guanidine alkaloids from Plumbago zeylanica

Five undescribed guanidine alkaloids, plumbagines HK (1-4) and plumbagoside E (5), as well as five known analogues (6-10) were isolated from the roots of Plumbago zeylanica. Their structures were established by extensive spectroscopic analyses and chemical methods. In addition, 1-10 were accessed their anti-inflammatory activities by measuring nitric oxide (NO) concentrations in LPS-induced RAW 264.7 cells. However, all compounds especially 1 and 3-5 could not inhibit the secretion of NO but significant increase the secretion of NO. The result reminded us that 1-10 may become potential novel immune potentiators.

The Marine Guanidine Alkaloid Crambescidin 816 Induces Calcium Influx and Cytotoxicity in Primary Cultures of Cortical Neurons through Glutamate Receptors

Crambescidin 816 is a guanidine alkaloid produced by the sponge Crambe crambe with known antitumoral activity. While the information describing the effects of this alkaloid in central neurons is scarce, Cramb816 is known to block voltage dependent calcium channels being selective for L-type channels. Moreover, Cramb816 reduced neuronal viability through an unknown mechanism. Here, we aimed to describe the toxic activity of Cramb816 in cortical neurons. Since calcium influx is considered the main mechanism responsible for neuronal cell death, the effects of Cramb816 in the cytosolic calcium concentration of cortical neurons were studied. The alkaloid decreased neuronal viability and induced a dose-dependent increase in cytosolic calcium that was also related to the presence of calcium in the extracellular media. The increase in calcium influx was age dependent, being higher in younger neurons. Moreover, this effect was prevented by glutamate receptor antagonists, which did not fully block the cytotoxic effect of Cramb816 after 24 h of treatment but completely prevented Cramb816 cytotoxicity after 10 min exposure. Therefore, the findings presented herein provide new insights into the cytotoxic effect of Cramb816 in cortical neurons.

Netamines O-S, Five New Tricyclic Guanidine Alkaloids from the Madagascar Sponge Biemna laboutei, and Their Antimalarial Activities

In our continuing program to isolate new compounds from the Madagascar sponge Biemna laboutei, five new tricyclic guanidine alkaloids, netamines O - S (1-5, resp.), have been identified together with the known compounds netamine E (6) and mirabilin J (7). The structures of all new netamines were assigned on the basis of spectroscopic analyses. Their relative configurations were established by analysis of ROESY data and comparison with literature data. Netamines O, P, and Q, which were isolated in sufficient quantities, were tested for their cytotoxic activities against KB cells and their activities against the malaria parasite Plasmodium falciparum. Netamines O and Q were found to be moderately cytotoxic. Netamines O, P, and Q exhibited antiplasmodial activities with IC₅₀ values of 16.99 ± 4.12, 32.62 ± 3.44, and 8.37 ± 1.35 μM, respectively.