Synthesis of branched cyclomaltooligosaccharide carboxylic acids (cyclodextrin carboxylic acids) by microbial oxidation

Identification of Pathways for Production of D-Glucaric Acid by Pseudogluconobacter saccharoketogenes

Pseudogluconobacter saccharoketogenes produces glucaric acid from D-glucose via two pathways, i.e., through D-glucuronic acid or D-gluconic acid. These pathways are catalyzed by alcohol dehydrogenase, aldehyde dehydrogenase, and gluconate dehydrogenase. Although D-glucaraldehyde and L-guluronic acid are also theorized to be produced in pathways throsugh D-glucuronic acid and D-gluconic acid, respectively, no direct data to identify these intermediates have been reported. In this study, the intermediates were purified and identified as D-glucaraldehyde and L-guluronic acid. The substrate specificities of the three enzymes on these intermediates and their oxidation products were studied, and the roles of alcohol, aldehyde, and gluconate dehydrogenases in D-glucaric acid-producing pathways were elucidated using the intermediates. Additionally, the substrate specificities of alcohol and aldehyde dehydrogenases on some alcohols, aldehydes, and aldoses were determined. Alcohol dehydrogenase showed wide substrate specificities, whereas the substrates oxidized by aldehyde dehydrogenase were limited. A 30-L scale reaction using the resting cells of Rh47-3 revealed that D-glucaric acid was produced from D-glucose and D-gluconic acid in 60.3 mol% (7.0 g/L) and 78.6 mol% (22.5 g/L) yields, respectively.

Identification of Enzymes from Pseudogluconobacter saccharoketogenes Producing d-Glucaric Acid from d-Glucose

In 2004, the US Department of Energy listed d-glucaric acid as one of the top 12 bio-based chemicals and a potential biopolymer building block. In this study, we show that Pseudogluconobacter saccharoketogenes strains can produce d-glucaric acid from d-glucose, although in low yield because of the generation of the byproduct 2-keto-d-gluconic acid in large quantities. To improve d-glucaric acid yield, we generated Rh47-3, a P. saccharoketogenes IFO14464 mutant, which produced d-glucaric acid from d-gluconic acid and d-glucose with 81 and 53 mol% yields, respectively. Furthermore, the key enzymes involved in d-glucaric acid production, alcohol dehydrogenase (Ps-ADH), aldehyde dehydrogenase (Ps-ALDH), and gluconate 2-dehydrogenase (Ps-GADH), were purified and their roles in d-glucaric acid synthesis were evaluated. Ps-ADH and Ps-ALDH catalyzed d-glucaric acid production, which was mediated by d-gluconic acid and d-glucuronic acid pathways. In contrast, Ps-GADH inhibited d-glucaric acid production by promoting the formation of 2-keto-d-gluconic acid from d-glucose.

Efficient Synthesis of Glucosyl-β-Cyclodextrin from Maltodextrins by Combined Action of Cyclodextrin Glucosyltransferase and Amyloglucosidase

Instead of β-cyclodextrin (β-CD), branched β-CDs have been increasingly used in many aspects as they possess better solubility and higher bioadaptability. But most commercialized branched β-CDs were chemically synthesized. Thus, the glucosyl-β-cyclodextrin (G₁-β-CD) prepared via enzymatic approach could be a nice substitute. However, the yield of G₁-β-CD was low. Here, we reported a controlled two-step reaction to efficiently prepare G₁-β-CD from maltodextrins by β-cyclodextrin glucosyltransferase (β-CGTase) and amyloglucosidase (AG). Compared to the single β-CGTase reaction, controlled two-step reaction caused a yield increase of G₁-β-CD by 130%. Additionally, the percentage of G₁-β-CD was enhanced from 2.4% to 24.0% and the side products α-CD and γ-CD were hydrolyzed because of the coupling activity of β-CGTase. Thus, this controlled two-step reaction might be an efficient approach for industrial production of pure G₁-β-CD.

Cyclodextrin, a novel therapeutic tool for suppressing amyloidogenic transthyretin misfolding in transthyretin-related amyloidosis

TTR (transthyretin), a β-sheet-rich protein, is the precursor protein of familial amyloidotic polyneuropathy and senile systemic amyloidosis. Although it has been widely accepted that protein misfolding of the monomeric form of TTR is a rate-limiting step for amyloid formation, no effective therapy targeting this misfolding step is available. In the present study, we focused on CyDs (cyclodextrins), cyclic oligosaccharides composed of glucose units, and reported the inhibitory effect of CyDs on TTR amyloid formation. Of various branched β-CyDs, GUG-β-CyD [6-O-α-(4-O-α-D-glucuronyl)-D-glucosyl-β-CyD] showed potent inhibition of TTR amyloid formation. Far-UV CD spectra analysis showed that GUG-β-CyD reduced the conformational change of TTR in the process of amyloid formation. In addition, tryptophan fluorescence and 1H-NMR spectroscopy analyses indicated that GUG-β-CyD stabilized the TTR conformation via interaction with the hydrophobic amino acids of TTR, especially tryptophan. Moreover, GUG-β-CyD exerted its inhibitory effect by reducing TTR deposition in transgenic rats possessing a human variant TTR gene in vivo. Collectively, these results indicate that GUG-β-CyD may inhibit TTR misfolding by stabilizing its conformation, which, in turn, suppresses TTR amyloid formation.

[Pharmaceutical application of cyclodextrins as multi-functional drug carriers]

Owing to the increasingly globalized nature of the cyclodextrin (CyD)-related science and technology, development of the CyD-based pharmaceutical formulation is rapidly progressing. The pharmaceutically useful CyDs are classified into hydrophilic, hydrophobic, and ionic derivatives. Because of the multi-functional characteristics and bioadaptability, these CyDs are capable of alleviating the undesirable properties of drug molecules through the formation of inclusion complexes or the form of CyD/drug conjugates. This review outlines the current application of CyDs in drug delivery and pharmaceutical formulation, focusing on the following evidences. 1) The hydrophilic CyDs enhance the rate and extent of bioavailability of poorly water-soluble drugs. 2) The amorphous CyDs such as 2-hydroxypropyl-beta-CyD are useful for inhibition of polymorphic transition and crystallization rates of drugs during storage. 3) The delayed release formulation can be obtained by the use of enteric type CyDs such as O-carboxymethyl-O-ethyl-beta-CyD. 4) The hydrophobic CyDs are useful for modification of the release site and/or time profile of water-soluble drugs with prolonged therapeutic effects. 5) The branched CyDs are particularly effective in inhibiting the adsorption to hydrophobic surface of containers and aggregation of polypeptide and protein drugs. 6) The combined use of different CyDs and/or pharmaceutical additives can serve as more functional drug carriers, improving efficacy and reducing side effects. 7) The CyD/drug conjugates may provide a versatile means for the constructions of not only colonic delivery system but also site-specific drug release system, including gene delivery. On the basis of the above-mentioned knowledge, the advantages and limitations of CyDs in the design of advanced dosage forms will be discussed.

6-O-alpha-(4-O-alpha-D-glucuronyl)-D-glucosyl-beta-cyclodextrin: solubilizing ability and some cellular effects

Some physicochemical and biopharmaceutical properties of a new branched cyclodextrin, 6-O-alpha-(4-O-alpha-D-glucuronyl)-D-glucosyl-beta-cyclodextrin (GUG-beta-CyD), were investigated. The interaction of GUG-beta-CyD with drugs was studied by spectroscopic and solubility methods, and compared with those of parent beta-CyD and 6-O-alpha-maltosyl-beta-CyD (G(2)-beta-CyD). The hemolytic activity of GUG-beta-CyD on rabbit erythrocytes was lower than those of beta-CyD and G(2)-beta-CyD. GUG-beta-CyD and G(2)-beta-CyD showed negligible cytotoxicity on Caco-2 cells up to at least 0.1 M. The inclusion ability of GUG-beta-CyD to neutral and acidic drugs was comparable to or slightly smaller than those of beta-CyD and G(2)-beta-CyD, probably because of a steric hindrance of the branched sugar. On the other hand, GUG-beta-CyD showed greater affinity for the basic drugs, compared with beta-CyD and G(2)-beta-CyD, owing to an electrostatic interaction of its carboxylate anion with positive charge of basic drugs. Thus, GUG-beta-CyD may be useful as a safe solubilizing agent particularly for basic drugs.