(+)-proto-Quercitol, a natural versatile chiral building block for the synthesis of the α-glucosidase inhibitors, 5-amino-1,2,3,4-cyclohexanetetrols

Enantioselective Synthesis of Nabscessin C

Enantioselective synthesis of nabscessin C (1), an aminocyclitol amide with antimicrobial activity, is reported. Starting from myo-inositol, (+)-nabscessin C was synthesized in 12 isolation steps. Desymmetrization of 2-deoxygenated 4,6-dibenzylinositol was achieved using lipase from porcine pancreas (PPL), and the stereochemistry was established by X-ray crystallography. This method has the potential for synthesizing other cyclitol-derived compounds.

Asymmetric Synthesis of Nabscessin A from Inositol and d-Camphor

An enantiomer of nabscessin A (1), an aminocyclitol amide with antimicrobial activity, was synthesized from myo-inositol and dimethyl d-camphor acetal in 14 steps. Formal synthesis of natural nabscessin A was also achieved through the new approach to access both enantiomers of 4,5-di-O-benzyl-myo-inositol, derived from the same set of starting materials. This synthesis features utilizations of the existing framework of myo-inositol and a regioselective esterification.

Efficient and Highly Stereoselective Syntheses of (+)-proto-Quercitol and (-)-gala-Quercitol Starting from the Naturally Abundant (-)-Shikimic Acid

Efficient and highly stereoselective syntheses of (+)-proto-quercitol and (-)-gala-quercitol starting from the naturally abundant (-)-shikimic acid were described in this article. (-)-Shikimic acid was first converted to the key intermediate by eight steps in 53% yield. It was then converted to (+)-proto-quercitol by three steps in 78% yield and was also converted to (-)-gala-quercitol by five steps in 63% yield. In summary, (+)-proto-quercitol and (-)-gala-quercitol were synthesized from (-)-shikimic acid by 11 and 13 steps in 41 and 33% overall yields, respectively.

Facile synthesis of (-)-vibo-quercitol from maltodextrin via an in vitro synthetic enzymatic biosystem

(-)-vibo-Quercitol (VQ: 1L-1,2,4/3,5-cyclohexanepentol), a form of deoxyinositol, is an alternative chiral building block in the synthesis of bioactive compounds to control diabetes. In this study, an adenosine triphosphate-free in vitro synthetic enzymatic biosystem composed of five enzymes (including one enzyme for NADH regeneration) was constructed to produce VQ from maltodextrin in one-pot. After optimization of reaction conditions, 7.6 g/L VQ was produced from 10 g/L maltodextrin with a product yield (mol/mol) of 77%, and 25.3 g/L VQ with a purity of 87% was produced from 50 g/L maltodextrin through simple scaling up of this nonfermentative enzymatic biosystem. Therefore, this study provides an economical and environmentally friendly method for the envisioned quercitol biosynthesis.

Quercitol: From a Taxonomic Marker of the Genus Quercus to a Versatile Chiral Building Block of Antidiabetic Agents

Quercitol is a cyclohexanepentol that has been recognized as a biomarker of plants in genus Quercus, which includes oak. As a result of its glucose-like structure, it has been introduced as an alternative chiral building block in the synthesis of several bioactive compounds. Our continuing investigations on the synthesis of antidiabetic agents from quercitol have demonstrated that this chiral synthon can generate diverse structural features with improved hypoglycemic activity.

Biosynthesis and production of quercitols and their application in the production of pharmaceuticals: current status and prospects

(-)-vibo-Quercitol is a deoxyinositol (1L-1,2,4/3,5-cyclohexanepentol) that occurs naturally in low concentrations in oak species, honeydew honey, and Gymnema sylvestre. The author's research group recently reported that (-)-vibo-quercitol and scyllo-quercitol (2-deoxy-myo-inositol, 1,3,5/2,4-cyclohexanepentol), a stereoisomer of (-)-vibo-quercitol, are stereoselectively synthesized from 2-deoxy-scyllo-inosose by the reductive reaction of a novel (-)-vibo-quercitol 1-dehydrogenase in Burkholderia terrae and of a known scyllo-inositol dehydrogenase in Bacillus subtilis, respectively. The author's research group therefore identified two enzymes capable of producing both stereoisomers of deoxyinositols, which are rare in nature. (-)-vibo-Quercitol and scyllo-quercitol are potential intermediates for pharmaceuticals. In this review, the author describes the biosynthesis and enzymatic production of quercitols and myo-inositol stereoisomers and their application in the production of potential pharmaceuticals.

Identification and characterization of a novel (-)-vibo-quercitol 1-dehydrogenase from Burkholderia terrae suitable for production of (-)-vibo-quercitol from 2-deoxy-scyllo-inosose

(-)-vibo-Quercitol is a deoxyinositol (1L-1,2,4/3,5-cyclohexanepentol) that naturally occurs in oak species, honeydew honey, wines aged in oak barrels, and Gymnema sylvestre and is a potential intermediate for pharmaceuticals. We found that (-)-vibo-quercitol is stereoselectively synthesized from 2-deoxy-scyllo-inosose by the reductive reaction of a novel (-)-vibo-quercitol 1-dehydrogenase found in the proteomes of Burkholderia, Pseudomonas, and Arthrobacter. Among them, Burkholderia terrae sp. AKC-020 (40-1) produced a (-)-vibo-quercitol 1-dehydrogenase appropriate for synthesizing (-)-vibo-quercitol with a high diastereomeric excess. The enzyme was strongly induced in Bu. terrae cells when quercitol or 2-deoxy-scyllo-inosose was used as carbon source in the culture medium. The enzyme is NAD(H)-dependent and shows highly specific activity for (-)-vibo-quercitol and myo-inositol among the substrates tested. The enzyme gene (qudh) was obtained by PCR using degenerate primers based on the N-terminal and internal amino acid sequences of the purified enzyme, followed by thermal asymmetric interlaced PCR. The qudh gene showed homology with inositol 2-dehydrogenase (sharing 49.5% amino acid identity with IdhA from Sinorhizobium meliloti 1021). We successfully produced several recombinant (-)-vibo-quercitol 1-dehydrogenases and related enzymes identified by genome database mining using an Escherichia coli expression system. This revealed that scyllo-inositol dehydrogenase (IolX) in Bacillus subtilis can catalyze the reduction of 2-deoxy-scyllo-inosose to yield scyllo-quercitol, a stereoisomer of (-)-vibo-quercitol. Thus, we successfully identified two enzymes to produce both stereoisomers of deoxyinositols that are rare in nature.

N-Arylmethylaminoquercitols, a new series of effective antidiabetic agents having α-glucosidase inhibition and antioxidant activity

A new series of N-arylalkylaminoquercitols were synthesized by reductive amination of aminoquercitol bisacetonide 5 and a variety of aryl aldehydes. The targeted N-substituted aminoquercitols having phenolic moiety (7a-7c) displayed significantly enhanced α-glucosidase inhibition, which is 26-32 times more potent than that of the unmodified aminoquercitol 6. In addition, compounds 7a-7c also retained antioxidant activity with relatively more pronounced potency than their original phenolics. This recent finding suggests an approach to develop effective antidiabetic agents by incorporating antioxidative moiety into aminocyclitol core structure.

Potent chemical chaperone compounds for GM1-gangliosidosis: N-substituted (+)-conduramine F-4 derivatives

The development of chemical chaperones to decrease the inhibitory activity while increasing the enzyme enhancement activity is described.

A hydrophilic conjugate approach toward the design and synthesis of ursolic acid derivatives as potential antidiabetic agent

In this study, a series of novel ursolic acid (UA) derivatives were designed and synthesized successfully via conjugation of hydrophilic and polar groups at 3-OH and/or 17-COOH position.

Triterpene glycosides and other polar constituents of shea (Vitellaria paradoxa) kernels and their bioactivities

The MeOH extract of defatted shea (Vitellaria paradoxa; Sapotaceae) kernels was investigated for its constituents, and fifteen oleanane-type triterpene acids and glycosides, two steroid glucosides, two pentane-2,4-diol glucosides, seven phenolic compounds, and three sugars, were isolated. The structures of five triterpene glycosides were elucidated on the basis of spectroscopic and chemical methods. Upon evaluation of the bioactivity of the isolated compounds, it was found that some or most of the compounds have potent or moderate inhibitory activities against the following: melanogenesis in B16 melanoma cells induced by α-melanocyte-stimulating hormone (α-MSH); generation of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, against Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-teradecanoylphorbol 13-acetate (TPA) in Raji cells; t TPA-induced inflammation in mice, and proliferation of one or more of HL-60, A549, AZ521, and SK-BR-3 human cancer cell lines, respectively. Western blot analysis established that paradoxoside E inhibits melanogenesis by regulation of expression of microphthalmia-associated transcription factor (MITF), tyrosinase, and tyrosinase-related protein-1 (TRP-1) and TRP-2. In addition, tieghemelin A was demonstrated to exhibit cytotoxic activity against A549 cells (IC50 13.5 μM) mainly due to induction of apoptosis by flow cytometry. The extract of defatted shea kernels and its constituents may be, therefore, valuable as potential antioxidant, anti-inflammatory, skin-whitening, chemopreventive, and anticancer agents.

Quercitylcinnamates, a new series of antidiabetic bioconjugates possessing α-glucosidase inhibition and antioxidant

Antidiabetic agents possessing dual functions, α-glucosidase inhibition and antioxidant, have been accepted to be more useful than currently used antidiabetic drugs because they not only suppress hyperglycemia but also prevent risk of complications. Herein, we design antidiabetic bioconjugates comprising of (+)-proto-quercitol as a glucomimic and cinnamic analogs as antioxidant moieties. Fifteen quercitylcinnamates were synthesized by direct coupling through ester bond in the presence of DCC and DMAP. Particular quercityl esters 6a, 7a and 8a selectively inhibited rat intestinal maltase and sucrose 4-6 times more potently than their parents 6, 7 and 8. Of synthesized bioconjugates, 6a was the most potent inhibitor against maltase and sucrose with IC₅₀ values of 5.31 and 43.65 μM, respectively. Of interest, its inhibitory potency toward maltase was 6 times greater than its parent, caffeic acid (6), while its radical scavenging (SC₅₀ 0.11 mM) was comparable to that of commercial antioxidant BHA. Subsequent investigation on mechanism underlying inhibitory effect of 6a indicated that it blocked maltase and sucrose functions by mixed inhibition through competitive and noncompetitive manners.

Concise syntheses of potent chaperone drug candidates, N-octyl-4-epi-β-valinenamine (NOEV) and its 6-deoxy derivative, from (+)-proto-quercitol

Described are the efficient syntheses of β-galactose-type unsaturated carbasugar amine, N-octyl-4-epi-β-valienamine (1a, NOEV) and 6-deoxy NOEV (12), starting from (+)-proto-quercitol (2), which is readily provided by the bioconversion of myo-inositol. NOEV is a potent chemical chaperone drug candidate for G(M1)-gangliosidosis. An intermediate alkadiene benzoate was prepared from 2 in five steps, with the key step being a Wittig reaction with an enol ester. The 6-deoxy derivative 12 was conveniently synthesized from the versatile intermediate dibromo compound 6, which was also an intermediate in the synthesis of NOEV. Enzyme inhibition assays demonstrated that 12 possessed stronger inhibitory activity than the parent 1a, suggesting that the C-6 position of the 4-epi-β-valienamine-type inhibitor could have hydrophobic interactions at the β-galactosidase active site residues.

(+)-Pinoresinol is a putative hypoglycemic agent in defatted sesame (Sesamum indicum) seeds though inhibiting α-glucosidase

Defatted sesame seeds have been reported for hypoglycemic effect in mice and T2DM women. An attempted to identify active components responsible for this effect was conducted using α-glucosidase-guided fractionation, resulting in the isolation of various lignans. Of compounds isolated, only (+)-pinoresinol showed inhibitory activity against rat intestinal maltase with an IC(50) value of 34.3 μM. The kinetic study indicated that enzymatic hydrolysis of maltose is inhibited by (+)-pinoresinol through competitive and noncompetitive manners. However, a lower dissociation constant (k(i) 288 M) of EI complex suggested that competitive inhibition is predominant over noncompetitive mode (k'(i) 1342 M).

A rapid differentiation between oak honeydew honey and nectar and other honeydew honeys by NMR spectroscopy

An NMR-based approach for rapid differentiation of oak honeydew honey from all other honey types (floral and other honeydew honeys) was proposed. It is based on the identification of the signals of the protons and the carbon of the methylene group of quercitol in the (1)H and (13)C NMR spectra of honey. The presence of quercitol was supported by TOCSY spectroscopy. Quercitol is a deoxyinositol which is regarded as a good taxonomic marker for the genus Quercus. All samples of oak honeydew honey contained quercitol, while in floral honey samples and honeydew honeys from fir and spruce it was absent. In addition, the described approach is promising with respect to quercitol quantification in honey by qNMR.

Concise synthesis of (+)-conduritol F and inositol analogues from naturally available (+)-proto-quercitol and their glucosidase inhibitory activity

An effective synthesis of (+)-conduritol F, (+)-chiro- and (+)-epi-inositols from naturally available (+)-proto-quercitol is described. This synthetic method provides a concise synthesis of cyclitols in enantiomerically pure form. Of the synthesized cyclitols, (+)-conduritol F potently inhibits type I α-glucosidase with an IC(50) value of 86.1 μM, which is five times greater than the standard antidiabetic drug, acarbose.

De novo synthesis of polyhydroxyl aminocyclohexanes

The syntheses of 12 stereochemically diverse polyhydroxyl aminocyclohexane ("aminocyclitols") derivatives are described. These short syntheses require 2-5 steps from N-(2,4-cyclohexadien-1-yl)phthalimide, which is prepared in two steps from tricarbonyl(cyclohexadienyl)iron(1+). The relative stereochemistries of the aminocyclitols were assigned by (1)H NMR spectroscopy as well as X-ray diffraction analysis.