Threonine crystallization

Purity Decrease of L-Threonine Crystals in Optical Resolution by Batch Preferential Ciystalli tion... 

DL-threonine and L-threonine crystals were supplied from Ajinomoto Co. Inc. and were used without further purification. Excess amounts of DL-threonine crystalline particles were dissolved in water kept at 55, 57, 58 or 60 C. After decantation and filtration each saturated solution was placed in the crystallizer maintained at 50 C. The difference between the saturation temperature and the crystallization temperature was defined as the initial supersaturation in terms of supercooling of the solution and was the driving force for the crystallization. 

This observation is in accordance with the phenomena of the crystallization in the resolution operation mentioned above in the following points. There are no clear, definite critical supersaturations above which nucleation of D-threonine occurs. Ohtsuki (2), however, reported supersolubility curve for this system, who gave the value of the supersaturation width At=7 C at 50 C. Their definition of the metastablllty was that no nucleation of the enantiomer other than seeded one was observed for two hours of resolution experiments. According to this definition, the supersolubility can be determined to lie somewhere between At=8 and 5 C from the present experimental data, this being in agreement with his result. If the crystallization proceeds further, however, D-threonine crystals may start to crystallize from the solution even if the initial supersaturation is 5 C. In this sense it is no longer the metastablllty limit. 

Batch crystallizers, applications, 102 Batch preferential crystallization, purity decrease of L-threonine crystals in optical resolution, 251-259 Bayer proce description, 329 Benzene, hi -pressure crystallization from benzene-cydohexane mixture, 281-289... 

Crystallization Method. Such methods as mechanical separation, preferential crystallisation, and substitution crystallisation procedures are included in this category. The preferential crystallisation method is the most popular. The general procedure is to inoculate a saturated solution of the racemic mixture with a seed of the desired enantiomer. Resolutions by this method have been reported for histidine (43), glutamic acid (44), DOPA (45), threonine (46), A/-acetyl phenylalanine (47), and others. In the case of glutamic acid, the method had been used for industrial manufacture (48). 

Phospho-L-threonine (L-threonine-O-phosphate) [1114-81-4] M 199.1, m 194 (dec), [a]p -7.37 (c 2.8, H2O) (pK as above). Dissolve in the minimum volume of H2O, add charcoal, stir for a few min, filter and apply onto a Dowex 50W (H" " form) then elute with 2N HCI. Evaporate the eluates under reduced pressure whereby the desired fraction produced crystals of the phosphate which can be recrystd from H2O-MeOH mixtures and the crystals are then dried in vacuo over P2O5 at 80 . [de Verdier Acta Chem Scand 7 196 7955.]... 

Figure 22. Photographs of (R,S)-serine crystals (a) Pure (b)-(d) grown in the presence of (b) (R)-threonine, (c) (S)-threonine, (d)-(R,5)-threonine (e) grown in the presence of resolved or (R,S) allothreonine.

These principles are nicely illustrated by the contrast between the serine-threonine and serine-allothreonine (allothr) systems. The relative orientation of molecular serine vis-a-vis its various crystal faces suggests that allothr can be adsorbed on the homotopic 100 faces as well as on the enantiotopic 011 faces (Figure 21). 

Nassar, N., Horn, G., Herrmann, C., Scherer, A., McCormick, F., and WiTTiNGHOFER, A., The 2.2 A crystal structure of the Ras-binding domain of the serine/threonine kinase c-RafL in complex with RaplA and a GTP analogue. Nature, 1995, 375, 554. 

The catalytic core of the proteasome is a threonine protease. Based on the crystal structure of the proteasome, it was concluded that proteasome functions through a new kind of proteolytic mechanism. In... 

In addition to the kink induced by the primary intercalating residue, a second kink two base steps away from the primary kink is revealed in the crystal structure of a complex of the HMG-D box with linear DNA [32]. The second kink arises from partial secondary intercalation in the minor groove of two adjacent residues, valine and threonine, immediately before the N-terminal end of helix II [32,42]. In the HMG boxes of HMGBl and 2, and other non-sequence-specific HMG proteins, a hydrophobic (and therefore potentially intercalating) residue is almost always found in the position corresponding to the valine in HMG-D [32,42] (residue Y in Table 1 and Fig. 2). In contrast, in the sequence-specific HMG... 

This mechanism has been supported by x-ray studies on crystallized xylose isomerase that suggest that the "active-site histidine" (presumed to be His 53, or 54 in some sequences) is located correctly so as to properly remove a proton from either Cl or C2 of the substrate, and that two threonine residues (Thr90 and Thr91, or 89,90 in some sequences) are positioned to provide polar oxygens to be either the acceptor or the donor proton in the cu-enediol configuration (57). 

In the optical resolution of DL-threonine mixtures by batch preferential crystallization, changes of solution concentration and crystal purity were measured. The mechanism of nucleation of the un-seeded enantiomer was discussed to explain the purity decrease of the resolved crystals. From the observation of crystallization behavior of the seed crystals of L-threonine, it was concluded that the existence of the D-enantiomer on the surface of the seed caused the sudden nucleation when they grew to attain sufficient amounts. 

After the solution temperature reached at 50 C 1 gram of the seed crystals were added to the solution, when the crystallization time is defined to be 0. Each crystallization was conducted for three hours. Samples of the solution and the crystalline particles were taken at every 30 minutes and their concentrations or purities of L-threonine were measured by the HPLC at least for two times. 

After the addition of the seed crystals the relative solution concentration was periodically measured. In Figure 3 the changes of L-threonine concentration in the solution were compared for four experimental runs with different initial supersaturations. Here the relative concentration is defined as the ratio of L-threonine to the total enantiomers. For the case of lower initial supersaturations... 

From the consecutive measurements of solution concentrations and crystal purities during the optical resolution by preferential crystallization, the crystallization of D-threonlne other than the seeded component (L-threonine) was observed In the later stage of the resolution. Washing of the seed crystals was found to be effective to delay the purity decrease. D-threonine was believed to be Introduced... 

Site-directed mutagenesis and the crystal structure analysis of a proteasome-inhibitor complex identified the amino-terminal threonine (Thrl) of Thermoplasma P subunits as both, the catalytic nucleophile and the primary proton acceptor (Seemiiller et al. 1995 Lowe et al. 1995). 

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