Leucrose

Leucrose, 6-0-(a-D-glucopyranosyl)-P-D-fmctopyranose [7158-70-5] is synthesized from sucrose usiag a dextranase enzyme from l euconostoc mesenteriodes and a small proportion of fmctose (2%). Pfeifer Langen of Germany have developed a production process for leucrose that iavolves extraction of the enzyme, treatment with 65% aqueous solution of sucrose and fmctose (1 2 wt/wt) at 25°C, separation of the product from fmctose by ion-exchange column chromatography, and crystallization. The product has not yet been launched on the market as of this writing (1996). 

Summarizing the results of many investigations, monosaccharides and such derivatives as D-mannitol and D-glucitol are rather weak acceptors. Disaccharides, including such acceptor products as isomaltose, are much better acceptors, except for certain molecules, for instance leucrose, which is not an acceptor.29,46,47 The decrease of enzyme activity with time has been described in terms of a first-order reaction. The inactivation parameters have been calculated for the immobilized enzyme. The inactivation constants kd were 0.0135 (1/d) when maltose was the acceptor (stabilizing), and 0.029 (1/d) when fructose was the acceptor.38... 

M. Boker, H. J. Jordening, and K. Buchholz, Kinetics of leucrose formation from sucrose by dextransucrase, Biotechnol. Bioeng., 43 (1994) 856-864. 

K. D. Reh, M. Noll-Borchers, and K. Buchholz, Productivity of immobilized dextransucrase for leucrose formation, Enzyme Microb. Technol., 19 (1996) 518-524. 

K. Buchholz, M. Noll-Borchers, and D. Schwengers, Production of leucrose by dextransucrase, Starch Starke, 50 (1998) 164—172. 

Disaccharides cellobiose and cellobiulose, (gentiobiose, isomaltose, kojibiose, laminarabiose, leucrose, melibiose, nigerose, palatinose, sophorose, trehalose, turanose, and xylobiose), lactose and lactulose, maltose and maltulose ... 

Maltose isomaltose maltulose melezitose leucrose kojibiose nigerose ... 

Figure 4. Hydroxyl PMR signals (solvent, methyl sulfoxide-d6) for A) D-fructose after prior equilibration in water B) D-fructose at equilibrium in methyl sulfoxide-d6 C) leucrose, freshly dissolved crystals D) furanose, freslily dissolved crystals (arrows show the positions of signals that increase in intensity with time) G2-hydroxyl proton-2, F4-hydroxul proton-4 E) lactulose, freshly dissolved crystals. At the upper right are 13C-2 signals at 25.15 MHz for D-fructose in water (see Reference...

The reaction is essentially irreversible. The main products are a high-molecular-weight (1 X 107— 1 X 10 Da) glucan, together with fructose, and the minor products are glucose and leucrose (where, n m or w). Glucose arises from an acceptor reaction with water, and leucrose [5-O-a-D-glucopyranosyl-D-fructopyr-anose] arises from an acceptor reaction with the primary product, fructose. (The acceptor reactions are discussed in Section IV.)... 

Fig. 8.—Thin-layer chromatographic autoradiogram of the acceptor products formed in the reaction of B-512FM dextransucrase with [14C]sucrose and D-glucose. The first acceptor product of D-glucose is isomaltose, followed in decreasing amounts by isomaltotriose through isomaltooctaose. A small amount of leucrose results from the acceptor reaction of D-fructopyranose. Dextran remains at the origin.

Even though the reaction scheme is complex, attempts have been made to model the reaction and develop kinetic equations. Mooser et al.lu developed kinetic equations for a limited case based on the primer mechanism. Reh et a/.145 developed kinetic equations for the synthesis of dextran and for the maltose acceptor reaction based on the two-site insertion mechanism. Likewise, Boker et al,146 developed a kinetic equation for the formation of the fructose acceptor product, leucrose, based on the two-site insertion mechanism that included an acceptor site. An equation was derived for the overall reaction rate that was a function of the consumption of sucrose by dextran formation and acceptor-product formation. 

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