Steroidal glycoalkaloid content of potato,tomato and their somatic hybrids

Summary Analyses of leaves and ‘tubers’ from somatic hybrids of potato and tomato (‘pomato’ with plastids of potato, ‘topato’ with plastids of tomato) produced by fusion of protoplasts from liquid cultures of dihaploid potato and mesophyll of tomato revealed the presence of the two major potato glycoalkaloids (α-solanine and α-chaconine) as well as the tomato glycoalkaloid (αtomatine). The total alkaloid content of leaves was greater than that of ‘tubers’ and similar to levels in the foliage of parent plants. However, glycoalkaloids were more abundant in hybrid ‘tubers’ than in normal potato tubers by a factor of 5–15. In hybrid foliage, approximately 98% of the alkaloid present was of potato origin whereas in ‘tubers’ the reverse was the case, with tomatine comprising 60–70% of the total alkaloid. The similarities in alkaloid content and ratios between the pomato and the topato lines indicate that plastomes do not influence the biosynthesis and distribution of these alkaloids. The results indicate that major secondary metabolites may prove useful for assessing the hybrid nature of such plants.     

Oxidative radical cyclizations of diketopiperazines bearing an amidomalonate unit. Heterointermediate reaction sequences toward the asperparalines and stephacidins

Abstract

A novel approach to the diazabicyclo[2.2.2]octane core of prenylated bridged diketopiperazine alkaloids is described by direct oxidative cyclizations of functionalized diketopiperazines mediated by ferrocenium hexafluorophosphate or the Mn(OAc)₃?2H₂O/Cu(OTf)₂ system. Divergent reaction pathways take place depending on the substitution pattern of the substrates and the oxidation conditions such as temperature or the presence or absence of persistent radical TEMPO. For ester-substituted diketopiperazines, the ester group exerts a significant influence on the reaction outcome and stereochemistry of the radical cyclizations.     

Chemical constituents from the aerial parts of Meconopsis horridula (Papaveraceae)

Chemical investigation of the aerial parts of Meconopsis horridula led to the isolation and structural identification of nine flavonoids, two alkaloids and five terpenoids. Their structures were determined by comparison of ¹H and ¹³C NMR data with those reported in literature. The discovery of alkaloid cavidilinine (11) and two pentacyclic triterpenoids (15 and 16) from M. horridula provides evidence to support the view that Fumarioideae and Papaveroideae should be combined into a single family Papaveraceae.     

Response of passerine birds and chicks to larvae and pupae of ladybirds

1. Few, if any, experimental tests have demonstrated the anti‐predator protection of the developmental stages of ladybirds (Coleoptera: Coccinellidae) against vertebrates, despite the fact that both the visual appearance of ladybirds and the content of defensive compounds fulfil the definition of an aposematic prey. 2. In this study, avian predators of three species were confronted with fourth‐instar larvae and pupae of the harlequin ladybird (Harmonia axyridis) – a large, conspicuous, and toxic ladybird species. 3. The selected predators differed in their individual experience and attitude to ladybirds. Wild‐caught great tits (Parus major) strongly avoided attacking ladybirds in general, whereas wild‐caught tree sparrows (Passer montanus) were willing to include ladybirds in their diet. Domestic chicks (Gallus gallus domesticus) have never been confronted with ladybirds but usually show avoidance of aposematic signals. In this study, great tits and domestic chicks avoided both developmental stages, but in the case of chicks the avoidance had to be learned over the course of repeated encounters. Sparrow avoidance was significantly lower, with more than one‐third of the prey being attacked and eaten. 4. The protection of both developmental stages of ladybirds is similar to adults, despite substantially different visual appearance.     

Multiple shoot cultures of Ophiorrhiza rugosa var. decumbens Deb and Mondal – A viable renewable source for the continuous production of bioactive Camptotheca alkaloids apart from stems of the parent plant of Nothapodytes foetida (Wight) Sleumer

Camptotheca alkaloids were isolated from multiple shoot cultures of O. decumbens (0.056% dry weight) and stems of N. foetida. The cytotoxicity of the extracts and products were tested in a panel of five cell lines. Crude extract from O. decumbens (Cr-Od) and N. foetida (Cr-Nf) showed more potent cytotoxic activity as compared to the isolated camptothecin from O. decumbens (CPT-Od) and N. foetida (CPT-Nf). CPT isolated from shoot cultures contained biological activity suggesting the possibility of using this system of O. decumbens as a renewable source for the production of camptotheca alkaloids. 9-Methoxy camptothecin (9-mCPT), isolated from N. foetida, was a very effective cytotoxic agent as compared to Cr-Nf or CPT-Nf. The IC₅₀ of 9-mCPT was 0.84, 0.32, and 0.35 μg/ml for A549, MCF7 and Jurkat cell lines and >3 μg/ml for U937. Viability assays using MTT dye were further confirmed by assessing extent of apoptosis in these cells. These findings suggest that shoot cultures of O. decumbens offer a rich alternative plant source for the anticancer compound, CPT and 9-mCPT is a more potent compound in N. foetida as compared to CPT.     

Stabilizing parallel G-quadruplex DNA by a new class of ligands: Two non-planar alkaloids through interaction in lateral grooves

Human DNA sequences consisting of tandem guanine (G) nucleotides can fold into a four-stranded structure named G-quadruplex via Hoogsteen hydrogen bonding. As the sequences forming G-quadruplex exist in essential regions of eukaryotic chromosomes and are involved in many important biological processes, the study of their biological functions has currently become a hotspot. Compounds selectively binding and stabilizing G-quadruplex structures have the potential to inhibit telomerase activity or alter oncogene expression levels and thus may act as antitumor agents. Most of reported G-quadruplex ligands generally have planar structures which stabilize G-quadruplex by π–π stacking. However, based on a pharmacophore-based virtual screening two non-planar G-quadruplex ligands were found. These two ligands exhibit good capability for G-quadruplex stabilization and prefer binding to paralleled G-quadruplex rather than to duplex DNA. The binding of these ligands to G-quadruplex may result from groove binding at a 2:1 stoichiometry. These results have shown that planar structures are not essential for G-quadruplex stabilizers, which may represent a new class of G-quadruplex-targeted agents as potential antitumor drugs.