Trochelioid A and B,new cembranoid diterpenes from the Red Sea soft coral Sarcophyton trocheliophorum

Chemical investigations of the soft coral Sarcophyton trocheliophorum, has led to the isolation of six cembranoids, two of which are new, Trochelioid A (1) and B (2), and one, 16-oxosarcophytonin E (3) isolated from nature for the first time. Additionally, two have been isolated from S. trocheliophorum for the first time (4 and 6). Structures were elucidated by employing extensive NMR and HR-FAB-MS experimentation.     

Impact of off-road vehicles on soil and vegetation in a desert rangeland in Saudi Arabia

Off-road vehicle driving is considered as main contributor to land degradation in arid regions. This study examined the impact of off-road vehicles (ORV) on soil and vegetation in a natural recreational desert meadow of Raudhat Khuraim, Saudi Arabia. Vegetation canopy cover and plant height away from road tracks were assessed. Also, species density and canopy cover, bare ground cover and soil attributes were assessed in four microhabitats; tracks, inter-tracks, verges, and away from vehicle tracks (undisturbed natural areas). Results show that the cover of forbs and grasses was negatively associated with distance from road verges. It was observed that the height of woody species responded negatively to distance away from tracks. Cover of native species decreased under verge, inter-track and track microhabitats giving more opportunity for weeds to flourish. Bare ground was highest (60.7%) in tracks. ORV impact on soil bulk density was clear with an increase of 38% under tracks compared to soils of undisturbed natural vegetation and a similar decrease in porosity was observed. On the other hand, soil electrical conductivity was significantly higher (5.45 mS cm^?1) under disturbance compared to 1.32 mS cm^?1 in undisturbed natural vegetation. Organic matter and nitrogen were not affected significantly by ORV disturbance. The results emphasize that managing off-road vehicle driving is essential for conserving native vegetation.     

Synthesis of new 9-glycosyl-4,9-dihydropyrano [3,4-b]indole-1(3H)-ones as antibacterial agents

A series of new 9-glycosyl-4,9-dihydropyrano[3,4-b]indole-1(3H)-ones 3 was synthesized in moderate to low yields. 4,9-Dihydropyrano[3,4-b]indole-1(3H)-ones (1) were coupled with different acetobromoglycopyranoses 2 in refluxing toluene in the presence of silver oxide to afford one coupling product of the respective N-glycosides. α-L-Arabinopyranosides 3j and 3m were the most active glycosides among the tested compounds against certain Gram positive and Gram negative bacterial strains.     

l-Lysine Catabolism Is Controlled by l-Arginine and ArgR in Pseudomonas aeruginosa PAO1

In comparison to other pseudomonads, Pseudomonas aeruginosa grows poorly in l-lysine as a sole source of nutrient. In this study, the ldcA gene (lysine decarboxylase A; PA1818), previously identified as a member of the ArgR regulon of l-arginine metabolism, was found essential for l-lysine catabolism in this organism. LdcA was purified to homogeneity from a recombinant strain of Escherichia coli, and the results of enzyme characterization revealed that this pyridoxal-5-phosphate-dependent decarboxylase takes l-lysine, but not l-arginine, as a substrate. At an optimal pH of 8.5, cooperative substrate activation by l-lysine was depicted from kinetics studies, with calculated K_m and V_max values of 0.73 mM and 2.2 μmole/mg/min, respectively. Contrarily, the ldcA promoter was induced by exogenous l-arginine but not by l-lysine in the wild-type strain PAO1, and the binding of ArgR to this promoter region was demonstrated by electromobility shift assays. This peculiar arginine control on lysine utilization was also noted from uptake experiments in which incorporation of radioactively labeled l-lysine was enhanced in cells grown in the presence of l-arginine but not l-lysine. Rapid growth on l-lysine was detected in a mutant devoid of the main arginine catabolic pathway and with a higher basal level of the intracellular l-arginine pool and hence elevated ArgR-responsive regulons, including ldcA. Growth on l-lysine as a nitrogen source can also be enhanced when the aruH gene encoding an arginine/lysine:pyruvate transaminase was expressed constitutively from plasmids; however, no growth of the ldcA mutant on l-lysine suggests a minor role of this transaminase in l-lysine catabolism. In summary, this study reveals a tight connection of lysine catabolism to the arginine regulatory network, and the lack of lysine-responsive control on lysine uptake and decarboxylation provides an explanation of l-lysine as a poor nutrient for P. aeruginosa.Decarboxylation of amino acids, including lysine, arginine, and glutamate, is important for bacterial survival under low pH (2, 7, 19). Lysine is abundant in the rhizosphere where fluorescent Pseudomonas preferentially resides, and serves as a nitrogen and carbon source to these organisms (28). In microbes, lysine catabolism can be initiated either through monooxygenase, decarboxylase, or transaminase activities. The monooxygenase pathway has been considered the major route for l-lysine utilization in Pseudomonas putida, and davBATD encoding enzymes for the first four steps of the pathway have been characterized (25, 26). In contrast, Pseudomonas aeruginosa cannot use exogenous l-lysine efficiently for growth (5, 24). It has been reported that enzymatic activities for the first two steps of the monooxygenase pathway are not detectable in P. aeruginosa, and no davBA orthologs can be identified from this organism (24, 25).Mutants of P. aeruginosa with improved growth on l-lysine and a high level of lysine decarboxylase activity can be isolated by repeated subcultures in l-lysine (5). This suggests that in P. aeruginosa, l-lysine utilization might be mediated by the lysine decarboxylase pathway with cadaverine and 5-aminovalerate as intermediates (Fig. ​(Fig.1).1). Alternatively, conversion of l-lysine into 5-aminovalerate may also be accomplished by a coupled reaction catalyzed by AruH and AruI. The AruH and AruI enzymes were reported as arginine:pyruvate transaminase and 2-ketoarginine decarboxylase, respectively (36). Interestingly, transamination by AruH using l-lysine as an amino group donor can also be detected in vitro (35). The reaction product α-keto-ɛ-aminohexanonate can potentially be decarboxylated into 5-aminovalerate by AruI, providing an alternative route for lysine degradation.Open in a separate windowFIG. 1.Lysine catabolic pathways. l-lysine decarboxylase pathway is shown at center. Broken arrows represent lysine monooxygenase pathway from P. putida which is not present in P. aeruginosa.In this study, we showed that the lysine decarboxylase pathway is the main route for lysine utilization under arginine control. Expression of the ldcAB operon encoding l-lysine decarboxylase and a putative lysine/cadaverine antiporter was analyzed regarding its response to l-lysine, l-arginine, and the arginine-responsive regulator ArgR. Enzyme characterization was performed to verify the function of LdcA as l-lysine decarboxylase. Arginine control on lysine incorporation was also investigated by genetic studies and uptake experiments. The peculiar role of ArgR controlling arginine and lysine uptake and catabolism provides the explanation for poor growth in lysine, and it implies a higher level of complexity in metabolic networks of pseudomonads.     

Biotransformation of sesquiterpenoids having α,β-unsaturated carbonyl groups with cultured plant cells of Marchantia polymorpha

The biotransformation of sesquiterpenoids having an α,β-unsaturated carbonyl group, such as α-santonin (1), lancerodiol p-hydroxybenzoate (2), 8,9-dehydronootkatone (3), and nootkatone (4), with cultured suspension cells of Marchantia polymorpha was investigated. It was found that the CC double bond of 1 and 2 was hydrogenated to give 1,2-dihydro-α-santonin (5) and 3,4-dihydrolancerodiol p-hydroxybenzoate (6), respectively, while the allylic position of the CC double bond of 3 and 4 was hydroxylated to give 13-hydroxy-8,9-dehydronootkatone (7) and 9-hydroxynootkatone (8), respectively.     

Constituents of Chrysothamnus viscidiflorus

A phytochemical investigation of the aerial parts of Chrysothamnus viscidiflorus var. viscidiflorus afforded three new [chrysothol (1), 2 and 4] and seven known compounds, including five sesquiterpenes, two cinnamic acid derivatives, two ketoalcohol derivatives and one coumarin glucoside. The structures of two previously reported compounds, 1b and 1c, were revised on the basis of chemical reaction. Structures of the compounds were determined by extensive NMR studies, including DEPT, COSY, NOE, HMQC, HMBC and X-ray analysis. The unpublished X-ray data of the known compounds 6 and 7 are reported. Compounds chrysothol (1), and 8-10 showed anti-cancer activity against human breast cancer cells.