Jungui Dai

2-(2-phenylethyl)chromones from Chinese eaglewood.

2-(2-Phenylethyl) chromones and a 2-(2-phenylethenyl) chromone, were isolated from the ethanolic extract of Chinese eaglewood. Their structures were determined on the basis of extensive analyses of spectroscopic data. Among those, one showed significant neuroprotective activities against both glutamate-induced and corticosterone-induced neurotoxicity in P12 pheochromocytoma and human U251 glioma cells at a concentration of 10 μM and increased cell viability by 82.2% and 86.9%, respectively.

Periconiasins A–C, New Cytotoxic Cytochalasans with an Unprecedented 9/6/5 Tricyclic Ring System from Endophytic Fungus Periconia sp.

Periconiasins A-C (1-3), new cytochalasans with an unprecedented 9/6/5 tricyclic ring system, were isolated from the endophytic fungus Periconia sp. F-31. Their structures and absolute configurations were elucidated by extensive spectroscopic and X-ray crystallographic analyses. Their biosynthesis is proposed to occur from an unusual seven acetate/malonate polyketide backbone attached to one leucine moiety by a PKS-NRPS followed by Diels-Alder and other reactions. 1 and 2 showed significant cytotoxicity against human HCT-8 cancer cells.

Exploring the catalytic promiscuity of a new glycosyltransferase from Carthamus tinctorius.

The catalytic promiscuity of a new glycosyltransferase (UGT73AE1) from Carthamus tinctorius was explored. UGT73AE1 showed the capability to glucosylate a total of 19 structurally diverse types of acceptors and to generate O-, S-, and N-glycosides, making it the first reported trifunctional plant glycosyltransferase. The catalytic reversibility and regioselectivity were observed and modeled in a one-pot reaction transferring a glucose moiety from icariin to emodin. These findings demonstrate the potential versatility of UGT73AE1 in the glycosylation of bioactive natural products.

Probing the Catalytic Promiscuity of a Regio‐ and Stereospecific C‐Glycosyltransferase from Mangifera indica

The catalytic promiscuity of the novel benzophenone C-glycosyltransferase, MiCGT, which is involved in the biosynthesis of mangiferin from Mangifera indica, was explored. MiCGT exhibited a robust capability to regio- and stereospecific C-glycosylation of 35 structurally diverse druglike scaffolds and simple phenolics with UDP-glucose, and also formed O- and N-glycosides. Moreover, MiCGT was able to generate C-xylosides with UDP-xylose. The OGT-reversibility of MiCGT was also exploited to generate C-glucosides with simple sugar donor. Three aryl-C-glycosides exhibited potent SGLT2 inhibitory activities with IC50  values of 2.6×, 7.6×, and 7.6×10(-7)  M, respectively. These findings demonstrate for the first time the significant potential of an enzymatic approach to diversification through C-glycosidation of bioactive natural and unnatural products in drug discovery.

Periconianone A, a new 6/6/6 carbocyclic sesquiterpenoid from endophytic fungus Periconia sp. with neural anti-inflammatory activity.

Periconianone A (1), a polyoxygenated sesquiterpenoid with a new 6/6/6 tricarbocyclic skeleton, and periconianone B (2) were isolated from the endophytic fungus Periconia sp. Their structures and absolute configurations were elucidated by extensive spectroscopic analyses, calculated ECD, and single-crystal X-ray diffraction (Cu Kα). The biosynthesis of the unusual six-membered carbonic ring of 1 was postulated to be formed through intramolecular aldol condensation. Compounds 1 and 2 showed significant neural anti-inflammatory activity.

Pericoannosin A, a Polyketide Synthase–Nonribosomal Peptide Synthetase Hybrid Metabolite with New Carbon Skeleton from the Endophytic Fungus Periconia sp.

Four new polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) hybrid metabolites, pericoannosin A (1), with an unusual hexahydro-1H-isochromen-5-isobutylpyrrolidin-2-one skeleton, and three cytochalasans, periconiasins D-F (2-4), were isolated from the endophytic fungus Periconia sp. F-31. Their structures and absolute configurations were elucidated through extensive spectroscopic analyses, calculated ECD, and single-crystal X-ray diffraction (Cu Kα). A possible biogenetic pathway is proposed. Compounds 1 and 4 showed anti-HIV activity with IC50s of 69.6 and 29.2 μM, respectively.

Antidepressant Abietane Diterpenoids from Chinese Eaglewood

Ten new abietane diterpenoids, aquilarabietic acids A-J (1-10), and a new podocarpane diterpenoid, aquilarabietic acid K (11), were isolated from the petroleum ether and ethanol extracts of Chinese eaglewood. Among them, 3, 9, and 10 are artifacts. Their structures were established on the basis of data from extensive spectroscopic and X-ray diffraction analyses. Bioassay results indicated that 1 at 10 μM demonstrated remarkable antidepressant activity in vitro by inhibiting norepinephrine reuptake in rat brain synaptosomes by 81.4% and with an IC(50) value of 9.1 × 10(-7) M.

Molecular Characterization and Phylogenetic Analysis of Two Novel Regio-specific Flavonoid Prenyltransferases from Morus alba and Cudrania tricuspidata

Background: Plant flavonoid prenyltransferases (FPTs) transfer prenyl moiety to flavonoid cores and have previously been identified only in Leguminosae. Results: The newly identified moraceous FPTs, MaIDT, and CtIDT, are distantly related to leguminous FPTs and feature catalytic regioselectivity and promiscuity. Conclusion: MaIDT and CtIDT evolved independently from leguminous FPTs. Significance: These findings are valuable for identifying additional evolutionarily different non-Leguminosae FPTs. Prenylated flavonoids are attractive specialized metabolites with a wide range of biological activities and are distributed in several plant families. The prenylation catalyzed by prenyltransferases represents a Friedel-Crafts alkylation of the flavonoid skeleton in the biosynthesis of natural prenylated flavonoids and contributes to the structural diversity and biological activities of these compounds. To date, all identified plant flavonoid prenyltransferases (FPTs) have been identified in Leguminosae. In the present study two new FPTs, Morus alba isoliquiritigenin 3′-dimethylallyltransferase (MaIDT) and Cudrania tricuspidata isoliquiritigenin 3′-dimethylallyltransferase (CtIDT), were identified from moraceous plants M. alba and C. tricuspidata, respectively. MaIDT and CtIDT shared low levels of homology with the leguminous FPTs. MaIDT and CtIDT are predicted to be membrane-bound proteins with predicted transit peptides, seven transmembrane regions, and conserved functional domains that are similar to other homogentisate prenyltransferases. Recombinant MaIDT and CtIDT were able to regioselectively introduce dimethylallyl diphosphate into the A ring of three flavonoids with different skeleton types (chalcones, isoflavones, and flavones). Phylogenetic analysis revealed that MaIDT and CtIDT are distantly related to their homologs in Leguminosae, which suggests that FPTs in Moraceae and Leguminosae might have evolved independently. MaIDT and CtIDT represent the first two non-Leguminosae FPTs to be identified in plants and could thus lead to the identification of additional evolutionarily varied FPTs in other non-Leguminosae plants and could elucidate the biosyntheses of prenylated flavonoids in various plants. Furthermore, MaIDT and CtIDT might be used for regiospecific prenylation of flavonoids to produce bioactive compounds for potential therapeutic applications due to their high efficiency and catalytic promiscuity.

Molecular insights into the enzyme promiscuity of an aromatic prenyltransferase

Aromatic prenyltransferases (aPTases) transfer prenyl moieties from isoprenoid donors to various aromatic acceptors, some of which have the rare property of extreme enzymatic promiscuity toward both a variety of prenyl donors and a large diversity of acceptors. In this study, we discovered a new aPTase, AtaPT, from Aspergillus terreus that exhibits unprecedented promiscuity toward diverse aromatic acceptors and prenyl donors and also yields products with a range of prenylation patterns. Systematic crystallographic studies revealed various discrete conformations for ligand binding with donor-dependent acceptor specificity and multiple binding sites within a spacious hydrophobic substrate-binding pocket. Further structure-guided mutagenesis of active sites at the substrate-binding pocket is responsible for altering the specificity and promiscuity toward substrates and the diversity of product prenylations. Our study reveals the molecular mechanism underlying the promiscuity of AtaPT and suggests an efficient protein engineering strategy to generate new prenylated derivatives in drug discovery applications.

Structures and absolute configurations of penicillactones A-C from an endophytic microorganism, Penicillium dangeardii Pitt.

Penicillactones A-C (1-3) are structurally related natural products with a spirocyclic anhydride structure and were isolated from the endophytic fungus Penicillium dangeardii Pitt. Penicillactones B and C showed inhibition of the release of β-glucuronidase from polymorphonuclear leukocytes with ED50 values of 2.58 and 1.57 μM. A 2D INADEQUATE experiment of 1 was performed at natural abundance to confirm the arrangement of its carbon skeleton. The configurations of 1-3 were established through extensive NMR spectroscopic analysis, selective structural modifications, and CD analysis.