Preparation of <small>D</small>-Gulose from Disaccharide Lactitol Using Microbial and Chemical Methods

Transforming monosaccharides: Recent advances in rare sugar production and future exploration

Rare sugars are defined as monosaccharides and their derivatives that do not exist in nature at all or that exist in extremely limited amounts despite being theoretically possible. At present, no comprehensive dogma has been presented regarding how and why these rare sugars have deviated from the naturally selected monosaccharides. In this minireview, we adopt a hypothesis on the origin and evolution of elementary hexoses, previously presented by one of the authors (Hirabayashi, Q Rev Biol, 1996, 71:365-380). In this scenario, monosaccharides, which constitute various kinds of glycans in nature, are assumed to have been generated by formose reactions on the prebiotic Earth (chemical evolution era). Among them, the most stable hexoses, i.e., fructose, glucose, and mannose remained accumulated. After the birth of life, the "chemical origin" saccharides thus survived were transformed into a variety of "bricolage products", which include galactose and other recognition saccharides like fucose and sialic acid through the invention of diverse metabolic pathways (biological evolution era). The remaining monosaccharides that have deviated from this scenario are considered rare sugars. If we can produce rare sugars as we wish, it is expected that various more useful biomaterials will be created by using them as raw materials. Thanks to the pioneering research of the Izumori group in the 1990's, and to a few other investigations by other groups, almost all monosaccharides including l-sugars can now be produced by combining both chemical and enzymatic approaches. After briefly giving an overview of the origin of elementary hexoses and the current state of the rare sugar production, we will look ahead to the next generation of monosaccharide research which also targets glycosides including disaccharides.

Protecting group enabled stereocontrolled approach for rare-sugars talose/gulose via dual-ruthenium catalysis

We herein report a convenient and highly stereocontrolled approach for rare and vital ᴅ-talo and ᴅ-gulo sugars directly from economical ᴅ-galactal through dual ruthenium-catalysis. The stereo-divergent strategy involves Ru(III)Cl₃-catalyzed Ferrier glycosylation of ᴅ-galactal to give 2,3-unsaturated ᴅ-galactopyranoside, further selective functionalization of C-4 and C-6 position with diverse protecting groups and dihydroxylation with Ru(VIII)O₄ generated in situ providing access to talo/gulo isomers. The α-anomeric stereoselectivity and syn-diastereoselectivity in glycosylation-dihydroxylation steps have been predominantly achieved by judicious selection of stereoelectronically diverse protecting groups. The synthetic utility of the dual-ruthenium catalysis was demonstrated for efficiently assembling the ᴅ-talose and/or ᴅ-gulose sugars in natural products and bioactive scaffolds.

Sugar alcohols derived from lactose: lactitol, galactitol, and sorbitol

Lactose is a common natural disaccharide composed of galactose and glucose molecules. It is mainly found in the whey, the by-product of cheese and casein industries. As the supply of lactose far exceeds demand, a lot of lactose was discarded as the waste every year, which not only leads to resource waste, but also causes environmental pollution. Therefore, the deep processing of lactose as the feedstock has become a hot research topic. The lactose-derived sugar alcohols, including lactitol, sorbitol, and galactitol, have shown great potential applications not only in food manufacture, but also in pharmaceutical, cosmetic, and material fields. In this paper, we focus on the property, physiological effect, production, and application of the lactose-derived sugar alcohols. KEY POINTS: • The deep processing of lactose as the feedstock has become a hot research topic. • The lactose-derived sugar alcohols show great application values. • Recent advances in the lactose-derived sugar alcohols are reviewed.

Sugar alcohol-based polymeric gene carriers: Synthesis, properties and gene therapy applications

Advances in the field of nanomedicine have led to the development of various gene carriers with desirable cellular responses. However, unfavorable stability and physicochemical properties have hindered their applications in vivo. Therefore, multifunctional, smart nanocarriers with unique properties to overcome such drawbacks are needed. Among them, sugar alcohol-based nanoparticle with abundant surface chemistry, numerous hydroxyl groups, acceptable biocompatibility and biodegradable property are considered as the recent additions to the growing list of non-viral vectors. In this review, we present some of the major advances in our laboratory in developing sugar-based polymers as non-viral gene delivery vectors to treat various diseases. We also discuss some of the open questions in this field. STATEMENT OF SIGNIFICANCE: Recently, the development of sugar alcohol-based polymers conjugated with polyethylenimine (PEI) has attracted tremendous interest as gene delivery vectors. First, the natural backbone of polymers with their numerous hydroxyl groups display a wide range of hyperosmotic properties and can thereby enhance the cellular uptake of genetic materials via receptor-mediated endocytosis. Second, conjugation of a PEI backbone with sugar alcohols via Michael addition contributes to buffering capacity and thereby the proton sponge effect. Last, sugar alcohol based gene delivery systems improves therapeutic efficacy both in vitro and in vivo.

Cloning and expression of d-glucoside 3-dehydrogenase from Rhizobium sp. S10 in Escherichia coli and its application for d-gulose production

The novel isolated Rhizobium sp. S10 was identified as d-glucoside 3-dehydrogenase (G3DH) producing microbe. Therefore, the gene encoding for G3DH from Rhizobium sp. S10 was cloned and overexpressed in Escherichia coli strain JM109 as a soluble enzyme complex. The recombinant G3DH (rG3DH) was purified with relatively high specific activity of 38.54 U/mg compared to the previously characterized and cloned G3DHs. The purified rG3DH showed the highest activity at pH 7.0, 40 °C toward cellobiose. It can also oxidize a broad range of mono-disaccharides including saccharide derivatives. The glycosides oxidizing activity combined with chemical reaction, could produce d-gulose from lactitol via 3-ketolactitol.

Triacetonide of Glucoheptonic Acid in the Scalable Syntheses of d-Gulose, 6-Deoxy-d-gulose, l-Glucose, 6-Deoxy-l-glucose, and Related Sugars

Ease of separation of petrol-soluble acetonides derived from the triacetonide of methyl glucoheptonate allows scalable syntheses of rare sugars containing the l-gluco or d-gulo structural motif with any oxidation level at the C6 or C1 position of the hexose, usually without chromatography: meso-d-glycero-d-guloheptitol available in two steps is an ideal entry point for the study of the biotechnological production of heptoses.

β-d-Gulose

The title compound, C₆H₁₂O₆, a C-3 position epimer of d-galactose, crystallized from an aqueous solution, was confirmed as β-d-pyran­ose with a ⁴C₁ (C1) conformation. In the crystal, O—H⋯O hydrogen bonds between the hy­droxy groups at the C-1 and C-6 positions connect mol­ecules into a tape structure with an R₃³(11) ring motif running along the a-axis direction. The tapes are connected by further O—H⋯O hydrogen bonds, forming a three-dimensional network.

Threats and opportunities of plant pathogenic bacteria

Plant pathogenic bacteria can have devastating effects on plant productivity and yield. Nevertheless, because these often soil-dwelling bacteria have evolved to interact with eukaryotes, they generally exhibit a strong adaptivity, a versatile metabolism, and ingenious mechanisms tailored to modify the development of their hosts. Consequently, besides being a threat for agricultural practices, phytopathogens may also represent opportunities for plant production or be useful for specific biotechnological applications. Here, we illustrate this idea by reviewing the pathogenic strategies and the (potential) uses of five very different (hemi)biotrophic plant pathogenic bacteria: Agrobacterium tumefaciens, A. rhizogenes, Rhodococcus fascians, scab-inducing Streptomyces spp., and Pseudomonas syringae.