Unlocking the hydrolytic mechanism of GH92 α-1,2-mannosidases: computation inspires using C-glycosides as Michaelis complex mimics

The conformational changes in a sugar moiety along the hydrolytic pathway are key to understand the mechanism of glycoside hydrolases (GHs) and to design new inhibitors. The two predominant itineraries for mannosidases go via OS2  B2,5  1S5 and 3S  3H4  1C4. For the CAZy family 92, the conformational itinerary was unknown. Published complexes of Bacteroides thetaiotaomicron GH92 catalyst with a S-glycoside and mannoimidazole indicate a 4C1  4H5/1S5  1S5 mechanism. However, as observed with the GH125 family, S-glycosides may not act always as good mimics of GH’s natural substrate. Here we present a cooperative study between computations and experiments where our results predict the E5  B2,5/1S5  1S5 pathway for GH92 enzymes. Furthermore, we demonstrate the Michaelis complex mimicry of a new kind of C-disaccharides, whose biochemical applicability was still a chimera.

Anomeric 1,2,3-triazole-linked sialic acid derivatives show selective inhibition towards a bacterial neuraminidase over a trypanosome trans-sialidase

Sialic acid is the natural substrate for sialidases and its chemical modification has been a useful approach to generate potent and selective inhibitors. Aiming at advancing the discovery of selective Trypanosoma cruzi trans-sialidase (TcTS) inhibitors, we have synthesised a small series of anomeric 1,2,3-triazole-linked sialic acid derivatives in good yields and high purity via copper-catalysed azide-alkyne cycloaddition (CuAAC, click chemistry) and evaluated their activity towards TcTS and neuraminidase. Surprisingly, the compounds showed practically no TcTS inhibition, whereas ca. 70% inhibition was observed for neuraminidase in relation to the analogues bearing hydrophobic substituents and ca. 5% for more polar substituents. These results suggest that polarity changes are less tolerated by neuraminidase due to the big difference in impact of hydrophobicity upon inhibition, thus indicating a simple approach to differentiate both enzymes. Moreover, such selectivity might be reasoned based on a possible steric hindrance caused by a bulky hydrophobic loop that sits over TcTS active and may prevent the hydrophobic inhibitors from binding. The present study is a step forward in exploiting subtle structural differences in sialidases that need to be addressed in order to achieve a selective inhibition.

Chaetopsina aquatica sp. nov. (Hypocreales, Nectriaceae) from the River Nile, Egypt

A new species, Chaetopsina aquatica, collected from the River Nile, Sohag, Egypt, is described and illustrated. Phylogenetic analyses of the combined ITS and LSU rDNA placed the new species within Chaetopsina as a phylogenetically distinct species. Chaetopsina aquatica formed a basal clade to a node containing C. aurantisalinicola and C. penicillata. The new species is characterized by its longer conidia (20–35.2 × 5–8.5 μm on natural substrate, 27.5–41.5 × 5–7 μm in culture) than those reported in Chaetopsina species.

ANTI-DIABESITY PRINCIPLE FROM THE SEEDS OF PHYLLANTHUS EMBLICA L.

In recent years, pancreatic lipase inhibitor and α- glucosidase inhibitor have been highlighted as potential anti-diabesity principles. In the present study, seeds of Phyllanthus emblica L. (Family: Phyllanthaceae) was studied for anti-diabesity potential in terms of pancreatic lipase inhibitory activity, α-glucosidase inhibitory activity and antioxidant activity. At 100μg/ml concentration, pancreatic lipase inhibition of the methanolic extract using synthetic substrate obtained was 73.2±0.1% (IC50 59.1μg/ml), whereas pancreatic lipase inhibition using natural substrate was 87.9 ± 2.62%. α- glucosidase inhibition of the extract at 50μg/ml was measured as 94.4±0.37% (IC50 34.4μg/ml). The superoxide scavenging activity of the extract was found to be 81.5±0.41%. Interestingly, upon TLC fingerprinting, only one band with Rf 0.70 showed multifunctional activity. The phytochemical found to be present was an alkaloid. The results evidenced the presence of multifunctional smart molecule in methanolic extract of P. emblica L and showed an alkaloid as the component responsible for anti-diabesity potential.

Micromelanconis kaihuiae gen. et sp. nov., a new diaporthalean fungus from Chinese chestnut branches in southern China

Melanconis-like fungi are distributed in several families of Diaporthales, mainly Juglanconidaceae, Melanconidaceae, Melanconiellaceae and Pseudomelanconidaceae. A new Melanconis-like genus of Pseudomelanconidaceae was discovered on branches of Chinese chestnut (Castanea mollissima) in southern China, which was confirmed by both morphology and phylogenetic analysis of combined ITS, LSU, tef1a and rpb2 sequences. The new genus Micromelanconis is characterized by two types of conidia from natural substrate and manual media of PDA, respectively. Conidia from Chinese chestnut branches are pale brown, ellipsoid, multiguttulate, aseptate with hyaline sheath. While conidia from PDA plates are pale brown, long dumbbell-shaped, narrow at the middle and wide at both ends, multiguttulate, aseptate, and also with hyaline sheath. All Pseudomelanconidaceae species were only reported on tree branches in China until now. More interesting taxa may be discovered if detailed surveys on tree-inhabiting fungi are carried out in East Asia in the future.

Design, Synthesis, and Evaluation of Potential Carbamate Prodrugs of 5′-methylthioadenosine (MTA)*

5′-Methylthioadenosine (MTA) is a natural substrate of MTA phosphorylase (MTAP) and is converted to adenine via a salvage pathway for AMP production in normal healthy cells. The lack of MTAP expression in many solid tumors and hematologic malignancies compared to normal healthy cells has been explored in a potential therapeutic strategy to selectively target tumor cells using antimetabolites such as 5-fluorouracil (5-FU) and 6-thioguanine (6-TG) while protecting normal healthy cells with MTA. Herein, a series of carbamate prodrugs, namely the N-(alkyloxy)carbonyl-MTA derivatives 2a-f, was designed, synthesized, and evaluated as potential prodrugs of MTA. All carbamate prodrugs were stable in phosphate buffer, pH 7.4 at 37 °C. In the presence of mouse liver microsomes, the prodrugs were converted to MTA at varying rates with the hexyl and butyl carbamates 2a and 2b most readily activated (t1/2 of 1.2 and 9.4 h, respectively). The activation was shown to be mediated by carboxyesterases present in mouse liver microsomes.