Lactate derivatives reactions

Alkoxy acids" and esters" have been prepared from the corresponding chloro derivatives. Reaction of the hydroxyl group of methyl lactate with methyl iodide is brought about by silver oxide (65%). Alkylation of the isomeric hydroxy benzoic acids is readily accomplished. ... 

Ethyl lactate was used for diastereocontrol and asymmetric transmission in a sequential 2,3-Wittig-oxy-Cope rearrangement, affording product in 91% ee (eq 9). - 4 Excellent asymmetric induction has also been noted in the Lewis acid-mediated ene reaction of (5)-ethyl lactate-derived intermediates (eq 10). ... 

Several alternative auxiliaries for obtaining anti aldol products are available [26]. For example, the lactate-derived ketone (R)-39, as developed in our laboratories, displays high levels of stereocontrol in boron-mediated anti aldol reactions (Scheme 9-14) [27]. Simple manipulations of the aldol product 40 allows the gen-... 

The related lactate-derived ketones, 44 [27] and 45 [29], are useful auxiliaries for boron- and titanium-mediated syn aldol reactions, respectively (Scheme 9-14). The effect of the protecting group in both cases is notable. For ketone 44, the use of the boron chloride reagent unexpectedly afforded the syn adduct with good control... 

At the time, many unsuccessful attempts were made to improve the selectivity of the mismatched anti aldol reaction mentioned above, outlining the limitations of some chiral ligands or auxiliaries at overcoming inherent substrate bias in anti aldol reactions. Since the completion of this work, we have introduced the lactate-derived ketones (/ )- and (S)-39, which should now allow the stereoselective synthesis of the ebelactones. As shown in Scheme 9-75, each enantiomer of the parent ketone acts as a propionate equivalent with a covalently attached auxiliary which will overturn the facial bias of most aldehydes [27, 28]. 

Various epimerases acting on carbohydrate derivatives and acyl-CoA derivatives were demonstrated, purified, and characterized as reviewed previously1184. Lactate race-mase (E.C. 5.1.2.1) is the first racemase to he discovered (1 41. The mechanism of lactate racemase reaction was studied with the enzyme preparations partially purified from Clostridium butyricumll8S. Hiyama et al.[1861 highly purified the enzyme from Lactobacillus sake, but little is known about its enzymological properties. In contrast, mandelate racemase (E. C. 5.1.2.2) is the enzyme best characterized among various racemases and epimerases its tertiary structure and functional groups that participate directly in catalysis has been clarified. 

Magnesiocuprates react with lactate derivative 189 to give the corresponding (S)-2-methylalkanoic acids (202) in moderate yield, however, optical yields are quite impressive, with enantiomeric excesses ranging from 95 to 99% [74]. This is superior to reactions with corresponding tosylates or mesylates where highly competitive reduction or elimination processes predominate. 

Cycloaddition of chiral imines with diketene allows one to gain access to chiral lactams. An interesting example of this is the reaction of lactate-derived imine 573 with diketene, which produces a 7.3 1 mixture of 574 and 575 [117]. Chromatographic separation of the major isomer furnishes 574 with an enantiomeric excess of 96%. 

The aldol reaction with the lactate derivative was applied to the synthesis of citreoviral 78 (Scheme 8.12). The enolate of 72 was reacted with unsaturated aldehyde 73 to yield a,(3-dihydroxy-7,8-unsaturated imide 74 in a stereoselective manner. Adduct 74 was subjected to iodolactonization to accompany the removal of the chiral auxiliary to give 75 as a single isomer. Debenzylation was followed by etherification with the tertiary alcohol to provide the highly substituted furan 77 having all the chiral centers of the target molecule. The additional four-step sequence afforded citreoviral 78. 

SCHEME 8.11. The titanium-mediated aldol reactions of lactate derivatives. 

Paterson I, Wallace DJ, Velazquez SM. Studies in polypropionate synthesis high -rr-face selectivity in syn and anti aldol reactions of chiral boron enolates of lactate-derived ketones. Tetrahedron Lett. 1994 35 9083-9086. 

Paterson I. Polyketide synthesis using the boron-mediated, aniialdol reactions of lactate-derived ketones total synthesis of (-)-ACRL Toxin IIIB. Synthesis 1998 639-650. 

In most biochemical reactions the pH of the medium is close to 7 At this pH car boxylic acids are nearly completely converted to their conjugate bases Thus it is common practice m biological chemistry to specify the derived carboxylate anion rather than the carboxylic acid itself For example we say that glycolysis leads to lactate by way of pyruvate... 

This is true of skeletal muscle, particularly the white fibers, where the rate of work output—and therefore the need for ATP formation—may exceed the rate at which oxygen can be taken up and utilized. Glycolysis in erythrocytes, even under aerobic conditions, always terminates in lactate, because the subsequent reactions of pymvate are mitochondrial, and erythrocytes lack mitochondria. Other tissues that normally derive much of their energy from glycolysis and produce lactate include brain, gastrointestinal tract, renal medulla, retina, and skin. The liver, kidneys, and heart usually take up... 

The material balance was calculated for EtPy, ethyl lactates (EtLa) and CD by solving the set of differential equation derived form the reaction scheme Adam s method was used for the solution of the set of differential equations. The rate constants for the hydrogenation reactions are of pseudo first order. Their value depends on the intrinsic rate constant of the catalytic reaction, the hydrogen pressure, and the adsorption equilibrium constants of all components involved in the hydrogenation. It was assumed that the hydrogen pressure is constant during... 

The Davies group has described several examples of a rhodium-catalyzed decomposition of a diazo-compound followed by a [2+1] cycloaddition to give divinyl cyclopropanes, which then can undergo a Cope rearrangement. Reaction of the pyrrol derivative 6/2-51 and the diazo compound 6/2-52 led to the tropane nucleus 6/2-54 via the cyclopropane derivative 6/2-53 (Scheme 6/2.11) [201]. Using (S)-lactate and (R)-pari lolaclorie as chiral auxiliaries at the diazo compound, a diastereoselectivity of around 90 10 could be achieved in both cases. 

Several enzymes have been immobilized in sol-gel matrices effectively and employed in diverse applications. Urease, catalase, and adenylic acid deaminase were first encapsulated in sol-gel matrices [72], The encapsulated urease and catalase retained partial activity but adenylic acid deaminase completely lost its activity. After three decades considerable attention has been paid again towards the bioencapsulation using sol-gel glasses. Braun et al. [73] successfully encapsulated alkaline phosphatase in silica gel, which retained its activity up to 2 months (30% of initial) with improved thermal stability. Further Shtelzer et al. [58] sequestered trypsin within a binary sol-gel-derived composite using TEOS and PEG. Ellerby et al. [74] entrapped other proteins such as cytochrome c and Mb in TEOS sol-gel. Later several proteins such as Mb [8], hemoglobin (Hb) [56], cyt c [55, 75], bacteriorhodopsin (bR) [76], lactate oxidase [77], alkaline phosphatase (AP) [78], GOD [51], HRP [79], urease [80], superoxide dismutase [8], tyrosinase [81], acetylcholinesterase [82], etc. have been immobilized into different sol-gel matrices. Hitherto some reports have described the various aspects of sol-gel entrapped biomolecules such as conformation [50, 60], dynamics [12, 83], accessibility [46], reaction kinetics [50, 54], activity [7, 84], and stability [1, 80],... 

This enzyme [EC 1.1.1.96] catalyzes the reversible reaction of )3-(3,5-diiodo-4-hydroxyphenyl)lactate with NAD+ to produce )3-(3,5-diiodo-4-hydroxyphenyl)pyru-vate and NADH. The substrates for this enzyme must contain an aromatic ring with a pyruvate side chain (or lactate), the most active substrates being halogenated derivatives. Potential substrates with hydroxyl or amino groups in the 3 or 5 position are inactive. 

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