Dipeptide synthesis

Scheme 7.31 Lipases in P-dipeptide synthesis in organic solvents.

Many reports confirm notable reductions in reaction times when carrying out reactions under micro flow conditions. Concerning p-dipeptide synthesis, for example, a comparison between batch and micro-reactor processing was made for the reaction of Dmab-P-alanine and Fmoc-i-P-homophenylalanine [158]. While the micro reactor gave a 100% yield in 20 min, only about 5% was reached with the batch method. Even after 400 h, only 70% conversion was achieved. 

Organic synthesis [OS 15] Dipeptide synthesis by carbodiimide coupling using... 

Organic synthesis 16 [OS 16] Dipeptide synthesis using pentafluorophenyi O-activation... 

Organic synthesis 25 [OS 25] a-Dipeptide synthesis from (R]-2-phenylbutyric acid... 

Organic synthesis 26 [OS 2 a-Dipeptide synthesis from (S)-a-methylbenzylamine... 

FIGURE 10.2 An outline of dipeptide synthesis by the solid phase technique... 

Dipeptide Synthesis. The synthesis of tyrosyl-tyrosine and phenylalanine dimer was performed (29) using a modified liquid phase technique. 

In the thermolysin-catalyzed solid-to-solid dipeptide synthesis of equimolar amounts of Z-Gln-OH and H-Leu-NH2 as model substrates, the water content was varied from 0 to 600 mL water (mol substrate)-1 and enzyme concentration in the range 0.5-10 g (mol substrate)-1 to achieve 80% yield and initial rates of 5-20 mmol (s kg)-1 (Erbeldinger, 1998). When the water content is decreased from the 1.6-molal lowest substrate concentration, the initial rate increases tenfold to a pronounced optimum at 40 mL water (mol substrate)-1 and falls to much lower values in a system with no added water, and to zero in a rigorously dried system. The behavior at a higher water content was demonstrated through variation of the enzyme content to be caused by mass transfer limitations at low water levels, the effects reflect the stimulation of the enzymatic activity by water. Preheating of the substrates or ultrasonic treatment had no significant effect on the system. 

Following the dipeptide synthesis from O-methyl-serine and Val by determining the loss 180 from di[180]valine, evidence for both reactions was obtained, but a direct reaction of Cys-AMP with free Val cannot be excluded [reaction (15)]. 

Fig. 6.15. Carboxylic acid activation with DCC. [1,3] means the intramolecular substitution of the oxygen atom 01 by the N atom "3" via a cyclic four-membered tetrahedral intermediate. From the point of view of the heteroatoms, this SN reaction corresponds to a migration of the acyl group R-C=0 from the oxygen to the nitrogen. (Examples for amino acid activations in the form of the pentafluorophenyl ester C or the benzotriazolyl ester D are given in Figure 6.32 (oligopeptide synthesis) and Figure 6.31 (dipeptide synthesis), respectively.

Eledroosmotic flow (EOF) conditions were applied and yielded only 10% conversion with constant reactant movement [9]. The use of stopped-flow techniques, which periodically push and mix the flow, led to a 50% increase in yield. A change in the coupling agent from l-(3-dimethylaminopropyl)-3-ethyl-carbodiimide hydrochloride (EDCI) to dicyclohexylcarbodiimide (DCC) for reasons of limited solubility resulted in a 93% yield of the dipeptide. Batch P-dipeptide synthesis using EDCI gave a yield of 50% [6]. 

A reduction in reaction time by virtue of the improved transport properties in eledroosmotic-driven microreadors was demonstrated for the P-dipeptide synthesis using pentafluorophenyl O-activation. Fmoc-P-alanine was preactivated by introducing the pentafluorophenyl fundion as ester group [9]. Dmab-P-alanine and the pentafluorophenyl ester of Fmoc-P-alanine readed, and the synthesis of the corres-... 

Fig. 10 Enzyme-catalyzed dipeptide synthesis with a subsequent threonine - phenylalanine exchange to form a more stable assembly...

Due to their increased reactivity toward nucleophiles, dipeptide a-phenacyl esters are prone to piperazine-2,5-dione (DKP) formation. Coupling of amino acid phenacyl esters with an activated carboxy component for dipeptide synthesis often results in substantial cyclization of the amino acid phenacyl esters via Schiff base formation (Scheme... 

From all known CRC, carnosine first appeared in muscle maturation. Its transformation into N-acetylcamosine (heart), anserine or ophidine (skeletal muscles) depends on specific en2ymes, thus the amount, to which these compounds are accumulated within the muscle, depends on functional activity of muscle [17]. In brain, besides carnosine, homocamosine is also present, which is synthesized by the same enzyme camosyne synthase having similar affinity to both P-alanine and y-aminobutyric acid. Thus, the ratio between carnosine and its homolog in different regions of brain is defined by the accessibility of substrates for dipeptide synthesis. In whole, tissue specificity in distribution and accumulation of different CRC allows to suggest correlation between the biological features of CRC and functional specificity of different excitable tissues [18]. 

Many examples are to be found in the chemical or biochemical literature e.g. ultrasonically induced emulsification/mixing has been utilized in the two-phase enzymatic synthesis of dipeptides [11]. For the dipeptide synthesis shown in reaction (1) the source of ultrasound was an ultrasonic bath (38 kHz). The importance of sonication in such a system is that it promotes biphasic reaction in solvent mixtures such as petroleum ether/water which are not effective under conventional conditions (Table 2). 

PhjSbO mediates the dehydrative condensation of carboxylic acids with amines via Ph3Sb(OCOR)2 as reactive intermediates [146]. This catalytic system has been applied to dipeptide synthesis (Scheme 14.73) [147]. Treatment of olefins with a mixture of AcOH and P4S10 in the presence of Ph jSbO affords alkylthio esters [148]. 

Jonsson, A. A., Adlercreutz, P., and Mattiasson, B., Effects of subzero temperatures on the kinetics of protease catalyzed dipeptide synthesis in organic media, Biotechnol. Bioeng., 46, 429 36, 1995. 

The dipeptide synthesis with free thermolysin (2 mg/ml) was carried out in water 10 mM of CLCa at pH 6,8 and 20 °C. The yield of peptide was below 10%, due to some reaction byproducts coming from the hydrolysis of methyl ester group of the peptide and consequent product hydrolysis as is shown in the following reactions ... 

Figure 2. Time course of the dipeptide synthesis of Z-Tyr-Gly-NH2. Initial concentrations were [Z-Tyr-OMe] - 10 mM, [Gly-NH2] — 15mM. [DTAB] — 0.15 M in 1 5 n-hexanol and n-octane. o - 6.5...

Lipases are also known to catalyze amide formation. Thus in 1987 Margolin and Klibanov [40] showed the use of porcine pancreatic lipase (PPL) for dipeptide synthesis in organic solvents. West and Wong [41] investigated several lipases and esterases for dipeptide and tripeptide synthesis, with variable yields observed. Later, Kawashiro et al. [42] also studied the dimerization of phenylalanine with PPL. 

Barros, R.J., Wehtje, E., and Adlercreutz, P. (1999) Enhancement of immobilized protease catalyzed dipeptide synthesis by the presence of insoluble protonated nucleophile. Enzyme Microb. Technol., 24 (8-9), 480-488. 

J., and Ulbrich-Hofman, R. (2002) Boilysin and thermolysin in dipeptide synthesis a comparative study. Biotechnol. Appl. Biochem., 36, 71-76. 

Dipeptide synthesis. Among vanoo least problems due to racemization are oh are the 6-trifluoromethylbenzotriazole i Hydroxy-7-azabenzotriazole itself is an ef additional advantage of being a visual iM endpoint.]... 

Now we can proceed with the rest of this dipeptide synthesis ... 

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