Serine optical rotation

The physical properties of the synthetic glycosyl derivatives of l-asparagine, L-serine, and L-threonine are reported in Tables I-V. Derivatives characterized otherwise, but without m.p. and optical rotation, have also been included. Whenever more than one reference is given, the physical constants are taken from the references printed in bold letters. The abbreviations used in the m.p. column are as follows foam., foaming dec., decomposing and soft., softening. 

Aziridines can be detected by a color reaction with 4-(4 -nitrobenzyl)pyridine that was originally developed for the detection and/or determination of a wide range of alkylating substances. 58 It can be adapted to TLC. 59 60 Upon acid hydrolysis of aziridine-2-carboxylic acid containing peptides, as required for amino acid analysis, this amino acid is recovered as serine in varying yields. 47 Configurational characterization of aziridine-2-carboxylates is performed by NMR spectroscopy 47 51 61-63 and X-ray analysis. 61 In addition, optical rotation of the related benzyl Wtritylaziridine-2-carboxylate is also used 64 with [a]D —95.5 (c 1, THF) for the 25-enantiomer 44 as reference. 

It is possible that racemization of some of the amiiio aeids, such as cystine, serine, and threonine, occurs during extraction and accounts for some of the complexity of wool protein fractions (Lindley, unpublished observations, 1962). Performic acid, however, used in the preparation of the keratoses did not produce racemization in proteins (Hill and Smith, 1957). It has not proved possible to solve uneciuivocally the problem of whether or not the reduction and alkylation pi oceduros used in the preparation of SCM kerateiues cause racemization. Lindley (unpublished, 1961) has shown that S -carboxymethyl cysteine isolated from acid hydrolyzates of SCM kerateines is partially racemized as measured both by direct optical rotation procedures and also by the use of a C-S lyase enzyme which is specihe for the n-form (Schwinuner and Kjaer, 1960). Control experiments showed, however, that L-S-carboxymethyl cysteine itself is partially racemized on refluxing with 5 N acid, and when allowance was made for this it appeared that the amount of racemization attributable to the reduction and alkylation procedures was small (less than 5 %) even when the most drastic conditions (pH 12.5 and 50°C) were used to prepare the SCM kerateines. Since S-carboxymethyl cysteine in peptide combination may well racemize more readily on acid hydrolysis than does the free amino acid, even this may be an over-estimate, and it would seem unlikely therefore that racemization is a serious problem in SCM kerateines as presently prepared. 

Submitters report an optical rotation value for crude N-Boc-L-serine methyl... 

The optical rotation of the L-oxazolidine methyl ester was -46.7 (CHCI3, c 1.30). An essentially identical procedure emanating from N-Boc-D-serine methyl ester gave the corresponding D-oxazolidine methyl ester in 80% yield with a rotation of +53°. In either case further purification could be achieved with flash chromatography... 

Globomycin was obtained as colourless crystals of m.p. 115°C and optical rotation [a]o 0° (chloroform). Its structure was established by means of the degradations depicted in Scheme 7. Four amino acids were obtained by acid hydrolysis, glycine, serine, a//othreonine and alio-isoleucine. y4//othreonine and a//oisoleucine were identified by comparison with authentic samples. It was also observed that in the mass spectra of the trimethylsilyl derivatives of threonine and a//othreonine, the relative intensities of the ions m/z 218 and 219 were significantly different and could be used for identification. 

The mixture of amino acids released by complete hydrolysis of lipopeptin A was fractionated by ion-exchange chromatography. Each amino acid was isolated and the optical rotation determined. Two moles of L-aspartic acid and 1 mole each of L-glutamic acid, L-serine, l-threonine, N-methyl-L-phenylalanine, L-threo-p-hydroxyglutamic acid and N-methyl-L-aspartic acid were obtained. 

In all cases following the above formula, except when R = H, the a-carbon is substituted asymmetrically. As a result, optical activity appears, since the model cannot be superimposed on its mirror image (cf. Chapt. 1-4). We recognize two steric configurations, the d- and the n-series. The amino acids appearing in proteins are members of the L-series. Their a-carbons are substituted just as in L-alanine and L-serine (R = CH3 and CH2OH respectively). The direction of optical rotation is independent of the configuration. 

Table 3. Corrected optical rotation values for glucose and serine enantiomers in the presence of different sodium salts (maximum error is 0.060). p are estimated ion polarisabiKties in solution in A .

Studies on the amino acid composition of ferritin could have permitted the prediction that the helical conformation of the molecule could be very high. Indeed, ferritin is low in valine, isoleucine, threonine, serine, and especially proline residues (1.2% of all amino acid), which would seriously disrupt helical regions. Studies of the optical rotary dispersion properties of ferritin established that the molecule is likely to contain 50% helical conformation. Once iron is removed from ferritin, the optical changes indicate further folding of the molecules, and although one can use ammonium sulfate and chromotographic analysis to separate ferritins with various iron content the changes in iron content do not affect the rotation properties of ferritin. 

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