Threonine formula

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). 

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... 

Without consulting chapter figures, draw Fischer projection formulas for glycine, aspartate, leucine, isoleucine, methionine, and threonine. 

Threonine (Thr or T) ((2S,31( )-2-amino-3-hydroxybutanoic acid) has an aliphatic hydroxyl side chain and is classified as a polar, uncharged amino acid with the formula HOOCCH(NH2)CHOHCH3. Together with Ser and Tyr, Thr is one of the three proteinogenic amino acids bearing an alcohol group. Thr can be seen as a hydroxylated version of Val. With two chiral centers, Thr can exist in four possible stereoisomers, or two possible diastereomers of L-Thr. However, the name L-Thr is used for one single enantiomer, (2S, 3if)-2-amino-3-hydroxybutanoic acid. The second diastereomer (2S,3S), which is rarely present in nature, is called L- //o-Thr. 

We have seen examples of molecules with one chiral center that exist in two mirror-image configurations, which we call enantiomers. What happens when there is more than one chiral center How many stereoisomers should we expect Consider the stereoisomers of the important amino acid, threonine, (2-amino-3-hydroxybutanoic acid). For this substance, if we write all of the possible configurations of its two chiral carbons, we have four different projection formulas, 19-22, corresponding to four different stereoisomers ... 

Proceeding as we did for threonine, we can write four projection formulas for tartaric acid, 2,3-dihydroxybutanedioic acid, as shown by 23-26 ... 

The amino acids in Table 27.1 that have more than one stereogenic center are isoleucine and threonine. The stereogenic centers are marked with an asterisk in the structural formulas shown. 

Evaluation of the HH ROESY (c) verifies the amino acid sequence of the cyclopentapeptide lactone ring attached to C-9 of actinocin by means of the NOE induced spatial correlation signals la-belled a d in the formula C. The a- and (3-protons of threonine in both cyclopentapeptide lactone rings are sufficiently separated but close to each other. This applies to the other amino acid protons with the exception of TV-methylvaline, in which proton signals overlap (Table 55.1). Therefore, starting from the a- and [3-protons of threonine 8H = 4.61 and 5.75), the sequence Thr-Vai-Pro-Sar-MeVal attached to C-l of actinocin is similarly verified in the HH ROESY as shown in formula C. The connection Sar-MeVal is established by the spatial correlations d between the 72-protons of sarcosine and the A7-methyl-protons of 7V-methylvaline in both rings (SH = 4.71/2.92 and 4.78/2.89). 

L-Threonine L-2-Amino-3-hydroxybutyric Acid CH3CHCCOOH HOH NH2 C4H9NO3 Formula wt 119.12... 

In general the thiol proteases catalyze the hydrolysis of a variety of peptide, ester, and amide bonds of synthetic substrates. Employing the general formula R —NH—CHR—CO—X, cleavage of the —CO—X— bond has been demonstrated when R represents the side chain of glycine, threonine, methionine, lysine, arginine, citrulline, leucine, and tyrosine. 

Problem 36.8 Draw all possible stereoisomeric formulas for the amino acid threonine. Naturally occurring threonine gets its name from its relationship to the letrose threose on this basis which is the correct configuration for natural threonine ... 

CONHa) 7 it was also reported that there was a single N-terminal threonine molecule. Although no detailed amino acid composition has been reported for the purified thyrocalcitonin prepared by Gudmunds-son et al. (G4), it differs considerably from the formula given above in that no cystine or isoleucine has been detected (Ml). 

The methionine-, threonine-, vafine- and isoleucine-free infant formula XMTVl Analog is suitable for the... 

Figure 11 (continued) The 20 amino acids (a) the formulae and the symbols (three-letter and one-letter codes) that are used and (b) the absolute configurations of a general amino acid group and the side chains of threonine and isoleucine which contain asymmetric carbon atoms... 

Isoleucine and threonine both have two chiral centers. According to official nomenclature the names L-isoleucine and L-threonine both designate only one optically active diastereoisomer. The mirror images are named D-isoleucine and o-threonine, whereas the diastereoisomers are named l-and D-alloisoleucine and l- and D-allothreonine. The configurations of L-isoleucine and L-threonine are shown in the formulas in Table I. The table also contains notation of the configuration at the two centers according to the R,S system and according to traditional nomenclature for amino acids (lUPAC-IUB, 1975). 

For example in the case of threonine, the four stereoisomers would have the following formulae ... 

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