0-Methyl-threonine

Figure 8. Schematic representation of site-specific incorporation of 0-methyl-threonine into the 252 position of cytochrome P450cam by employing an in vitro transcription coupled translation system of Escherichia coli.

In all the above studies thiaisoleucine was tested with prokariotic organisms it seemed interesting to study its effects on protein synthesizing systems from rat liver and rabbit reticulocytes. It was first investigated the activation of thiaisoleucine by rat liver aminoacyl-tENA synthetases studying the aminoacid-dependent ATP-PPi exchange reaction(29). It was shown that thiaisoleucine, like 0-methyl-threonine,is a substrate for the enzyme. 

The Em values obtained,reported in Table III,showed that both analogs have a lower affinity than isoleucine for the synthetase,but thiaisoleucine has a three-fold greater aiffinity than 0-methyl-threonine. The V values were quite similar for isoleucine and for both the analogs. From the V values obtained when both isoleucine and thiaisoleucine were present together in 1 1 molar ratio,or when isoleucine was incubated in the presence of equimolar amoiints of leucine,it was concluded that thiaisoleucine is activated by isoleucyl-tENA synthetase. 

Km and V values for isoleucine,thiaisoleucine and 0-methyl-threonine in the ATP-PPi exchange reaction catalyzed by rat liver aminoacyl-tEKA synthetase. Experimental details in(29). V values expressed as per cent of that obtained with isoleucine. 

It was then tested if thiaisoleucine once activated could be transferred to tENA and this was done by assaying the effect of thiaisoleucine on the binding of labelled isoleucine to tENA. Eig.2 shows that thiaisoleucine and 0-methyl-threonine inhibit isoleucyl-tENA synthesis thiaisoleucine was ten times more effective than 0-methyl-threonine.It was also demonstrated that the inhibition was in both cases reversed by isoleucine. 

Fig.2. Inhibition of isoleucyl-tEHA synthesis by thiaisoleucine (full lines) and by 0-methyl-threonine (broken lines).Relative ILE incorporation = ratio of the amount of tERA-bound 2H-isoleucine in the presence of the indicated concentrations of the analogs to the amount in their absence. Experimental details in (29).

Per cent of inhibition of isoleucine and leucine incorporation into polypeptides by thiaisoleucine(T-ILE) and 0-methyl-threonine(O-MT).Experimental details in (29). 

Overall the results obtained show that all the enzymes involved in the various steps of isoleucine incorporation into proteins are effective also on thiaisoleucine. In other words the substitution of a carbon atom along the carbon chain of the substrate by a sulfur atom does not dramatically affect the substrate specificity of the enzymes. The comparative data obtained with 0-methyl-threonine indicated that the substitution of a canbon atom by an oxygen atom along the carbon chain affects the substrate specificity of the enzymes more than does the substitution by a sulfur atom. 

Uhlig, S., Ivanova, L., Petersen, D., Kristensen, R. (2009). Structural studies on minor enniatins from Fusarium sp. VI 03441 novel V-methyl-threonine containing enniatins. Toxicon, 53, 734—742. 

A more eflicient and general synthetic procedure is the Masamune reaction of aldehydes with boron enolates of chiral a-silyloxy ketones. A double asymmetric induction generates two new chiral centres with enantioselectivities > 99%. It is again explained by a chair-like six-centre transition state. The repulsive interactions of the bulky cyclohexyl group with the vinylic hydrogen and the boron ligands dictate the approach of the enolate to the aldehyde (S. Masamune, 1981 A). The fi-hydroxy-x-methyl ketones obtained are pure threo products (threo = threose- or threonine-like Fischer formula also termed syn" = planar zig-zag chain with substituents on one side), and the reaction has successfully been applied to macrolide syntheses (S. Masamune, 1981 B). Optically pure threo (= syn") 8-hydroxy-a-methyl carboxylic acids are obtained by desilylation and periodate oxidation (S. Masamune, 1981 A). Chiral 0-((S)-trans-2,5-dimethyl-l-borolanyl) ketene thioketals giving pure erythro (= anti ) diastereomers have also been developed by S. Masamune (1986). 

A second, conceptually distinct chiral synthesis of monobactams was developed from P-hydroxy amino acids. As shown in Figure 2, cycli2ation of the acylsulfamate of an amino-protected 0-mesylserine derivative (14, R = H) leads directiy to the monobactam (15). This methodology was also appHed to the synthesis of 4a- (15, R = CH ) and 4P-methyl monobactams from L-threonine and aHothreonine, respectively (17). The... 

Almost all actinomycins have the same chromophore, a planar phenoxa2inone dicarboxyUc acid called actinocin. In dactinomycin, the stmcture of which is shown in Figure 12, the two pendent pentapeptide lactones are identical, but in other actinomycins these lactones may be different. In other actinomycins the first amino acid, amide linked with actinocin, is usually L-threonine, as in dactinomycin the second position is sometimes D-aHo-isoleucine instead of D-valine the third position may be sarcosine or oxoproline the fourth position is sarcosine and the fifth position is sometimes /V-methyl isoleucine instead of /V-methylvaline. The lactone ring is always present. 

Amino-4,6-dimethyl-3-oxo-3//-phenoxazine-l,9-dicarboxylic acid also named actinocin is the chromophor of the red antineoplastic chromopeptide aetinomyein D (formula A). Two cyclopenta-peptide lactone rings (amino acids L-threonine, D-valine, L-proline, sarcosine, and 7V-methyl-L-valine) are attached to the carboxy carbons of actinocin by two amide bonds involving the amino groups of threonine. 

Quaternary salts of the substances represented by tliese formulae have been prepared by Kogl, Veldstra and van der Laan as well as of the next lower homologues, the substituted butyraldehydes, and the methyl ethers of both series. Their pharmacological activities were negligible in comparison with that of muscarine, but as six stereoisomeric forms may be produced in each synthesis, the inactivity may be due to stereoisomerism, just as in the case of threonine (a-amino-)3-hydroxy-butyric acid) where West and Carter found that only the d —) form is... 

Chiral enolates of 1,3-dioxalan-4-ones, methyl l,3-oxa2ohdine-4-carboxylates,and 1,3-iml-da2ohdine-4-ones derived from chiral natural sources such as fS -prohne, fS -serine, and fS -threonine are added to nltroalkenes in high diastereoselectivity fScheme 4,12, ... 

Isoleucine and threonine (Problem 26.3) are the only two amino acids with two chirality centers. Assign R or 5 configuration to the methyl-bearing carbon atom of isoleucine. 

This type of yvn-seleclivc aldol addition has been applied in the synthesis of the unusual L-threonine based amino acid, (2,S, 3/ ,6F)-3-hydroxy-4-methyl-2-methylamino-6-octenoic acid, of cyclosporine104, of the cyclic hexapeptide echinocandin105, and of the antibiotic ionomycin97. 

C4H9NO, 72-19-5) see Aztreonam L-threonine methyl ester hydrochloride (C5H12CINO, 39994-75-7) see Aztreonam thymidine... 

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