Three neo-Clerodane Diterpenoids from Tinospora cordifolia Stems and Their Arginase Inhibitory Activities.

Three neo-clerodane diterpenoids, including two new tinocordifoliols A (1) and B (2) and one known tinopanoid R (3), were isolated from the ethyl acetate-soluble fraction of the 70% ethanol extract of Tinospora cordifolia stems. The structures were elucidated by various spectroscopic methods, including one dimensional (1D) and 2D-NMR, high resolution-electrospray ionization (HR-ESI)-MS, and electronic circular dichroism (ECD) data. The T. cordifolia extract and all isolated compounds 1-3 possessed arginase I inhibitory activities. Among them, 3 exhibited moderate competitive inhibition of human arginase I (IC50 = 61.9 µM). Furthermore, docking studies revealed that the presence of a ß-substituted furan in 3 may play a key role in the arginase I inhibitory activities.

A Small-Molecule Inhibitor of Factor Inhibiting HIF Binding to a Tyrosine-Flip Pocket for the Treatment of Obesity.

In animals, limiting oxygen upregulates the hypoxia-inducible factor (HIF) and promotes a metabolic shift towards glycolysis. Factor inhibiting HIF (FIH) is an asparaginyl hydroxylase that regulates HIF function by reducing its interaction with histone acetyl transferases. HIF levels are negatively regulated by the HIF prolyl hydroxylases (PHDs) which, like FIH, are 2-oxoglutarate (2OG) oxygenases. Genetic loss of FIH promotes both glycolysis and aerobic metabolism. FIH has multiple non-HIF substrates making it challenging to connect its biochemistry with physiology. A structure-mechanism guided approach identified a highly potent in vivo active FIH inhibitor, ZG-2291, the binding of which promotes a conformational flip of a catalytically important tyrosine, enabling the selective inhibition of FIH over other Jumonji C subfamily 2OG oxygenases. Consistent with genetic studies, ZG-2291 promotes thermogenesis and ameliorates symptoms of obesity and metabolic dysfunction in ob/ob mice. The results reveal ZG-2291 as a useful probe for the physiological functions of FIH and identify FIH inhibition as a promising strategy for obesity treatment.

Substrate Flexibilities of Norbelladine Synthase and Noroxomaritidine/Norcraugsodine Reductase for Hydroxylated and/or Methoxylated Aldehydes.

Amaryllidaceae alkaloids are structurally diverse natural products with a wide range biological properties, and based on the partial identification of the biosynthetic enzymes, norbelladine would be a common intermediate in the biosynthetic pathways. Previous studies suggested that norbelladine synthase (NBS) catalyzed the condensation reaction of 3,4-dihydroxybenzaldehyde and tyramine to form norcraugsodine, and subsequently, noroxomaritidine/norcraugsodine reductase (NR) catalyzed the nicotinamide adenine dinucleotide phosphate (NADPH)-dependent reduction of norcraugsodine to generate norbelladine. However, recent studies have highlighted possible alternative Amaryllidaceae alkaloid biosynthetic pathways via the formation of isovanillin and vanillin from the 4-O- and 3-O-methylation reactions of 3,4-dihydroxybenzaldehyde, respectively. Herein, we focused on NpsNBS and NpsNR, which were initially identified from Narcissus pseudonarcissus, and explored their substrate recognition tolerance by performing condensation reactions of tyramine with various benzaldehyde derivatives, to shed light on the Amaryllidaceae alkaloid biosynthetic pathway from the viewpoint of the enzymatic properties. The assays revealed that both NpsNBS and NpsNR lacked the abilities to produce 4'-O- and 3'-O-methylnorbelladine from isovanillin and vanillin with tyramine, respectively. These observations thus suggested that Amaryllidaceae alkaloids are biosynthesized from norbelladine, formed through the condensation/reduction reaction of 3,4-dihydroxybenzaldehyde with tyramine.

Human Oxygenase Variants Employing a Single Protein FeII Ligand Are Catalytically Active.

Aspartate/asparagine-ß-hydroxylase (AspH) is a human 2-oxoglutarate (2OG) and FeII oxygenase that catalyses C3 hydroxylations of aspartate/asparagine residues of epidermal growth factor-like domains (EGFDs). Unusually, AspH employs two histidine residues to chelate FeII rather than the typical triad of two histidine and one glutamate/aspartate residue. We report kinetic, inhibition, and crystallographic studies concerning human AspH variants in which either of its FeII binding histidine residues are substituted for alanine. Both the H725A and, in particular, the H679A AspH variants retain substantial catalytic activity. Crystal structures clearly reveal metal-ligation by only a single protein histidine ligand. The results have implications for the functional assignment of 2OG oxygenases and for the design of non-protein biomimetic catalysts.