Abstract
Trehalose (α-d-glucopyranosyl α-d-glucopyranoside) is a non-reducing sugar with unique stabilizing properties due to its symmetrical, low energy structure consisting of two 1,1-anomerically bound glucose moieties. Many applications of this beneficial sugar have been reported in the novel food (nutricals), medical, pharmaceutical and cosmetic industries. Trehalose analogues, like lactotrehalose (α-d-glucopyranosyl α-d-galactopyranoside) or galactotrehalose (α-d-galactopyranosyl α-d-galactopyranoside), offer similar benefits as trehalose, but show additional features such as prebiotic or low-calorie sweetener due to their resistance against hydrolysis during digestion. Unfortunately, large-scale chemical production processes for trehalose analogues are not readily available at the moment due to the lack of efficient synthesis methods. Most of the procedures reported in literature suffer from low yields, elevated costs and are far from environmentally friendly. “Greener” alternatives found in the biocatalysis field, including galactosidases, trehalose phosphorylases and TreT-type trehalose synthases are suggested as primary candidates for trehalose analogue production instead. Significant progress has been made in the last decade to turn these into highly efficient biocatalysts and to broaden the variety of useful donor and acceptor sugars. In this review, we aim to provide an overview of the latest insights and future perspectives in trehalose analogue chemistry, applications and production pathways with emphasis on biocatalysis.
Highlights
Trehalose (α-D-glucopyranosyl α-D-glucopyranoside or α,α-trehalose) is a non-reducing disaccharide that consists of two 1,1-linked α-glucose monosaccharides (Figure 1a) and possesses interesting properties for the food and pharmaceutical industry [1]
The downside is that ingested trehalose contributes to the caloric intake as it can be efficiently hydrolysed in the small intestine by trehalases (α,α-trehalose-1-C-glucohydrolase, EC (Enzyme Commission) number 3.2.1.28), present in the intestinal villi, and absorbed in the form of glucose [3]
The traditional trehalose phosphate synthase/phosphorylase (TPS/TPP) route (a); the malto-oligosyltrehalose synthase/hydrolase (MTS/MTH)-coupled route (b); the TreS-type trehalose synthase route (c); the TreT-like trehalose synthase route (d); and the inverting (e) or retaining (f) trehalose phosphorylase (TP) routes coupled with other glycoside phosphorylases, i.e., maltose phosphorylase (MP) and sucrose phosphorylase (SP), respectively
Summary
Trehalose (α-D-glucopyranosyl α-D-glucopyranoside or α,α-trehalose) is a non-reducing disaccharide that consists of two 1,1-linked α-glucose monosaccharides (Figure 1a) and possesses interesting properties for the food and pharmaceutical industry [1]. Lactotrehalose (α-D-galactopyranosyl α-D-glucopyranoside), where the first glucose unit has been replaced by galactose (Figure 1b), is not a substrate for intestinal trehalase but functions as a competitive inhibitor of the same enzyme [4] This disaccharide does not contribute to the energy content of food preparations and at the same time lowers the metabolic conversion of trehalose. Unlike in humans, an essential metabolite for Mycobacteria, deoxy- or azido-derivatives of trehalose (Figure 1d) form valuable tools to inhibit mycobacterial cell growth or for future imaging and detection of Mycobacterium tuberculosis, the causative agent of tuberculosis [6] Despite their value, analogues of trehalose have not yet been studied very extensively because no cost-effective process for their large-scale synthesis is currently available. Alternative production routes for trehalose analogues have recently been explored, which will be extensively discussed and compared in this review
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