Threonine, periodate oxidation

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). 

Periodate Oxidation of N-Terminal Serine or Threonine Residues... 

Figure 1.107 The N-terminal aldehyde group on a peptide formed from periodate oxidation of serine or threonine residues can be conjugated with a hydrazide-containing molecule to produce a hydrazone bond.

Determination of Threonine by Oxidation with Periodate. J- biol. Chem. 142, 461 (1942). 

Unique methods based on new principles have been developed within the past 10 years. Threonine (27,28,249) is oxidized by lead tetraacetate or periodic acid to acetaldehyde, which is determined by photometric analysis of its p-hydroxydiphenyl complex or iodometric titration of its combined bisulfite. Serine is oxidized similarly to formaldehyde, which is determined gravimetrically (207) as its dimedon (5,5-dimethyldihydro-resorcinol) derivative or photometric analysis (31) of the complex formed with Eegriwe s reagent (l,8-dihydroxynaphthalene-3,5-disulfonic acid). It appears that the data obtained for threonine and serine in various proteins by these oxidation procedures are reasonably accurate. [Block and Bolling (26) have given data on the threonine and serine content of various proteins. ]... 

Figure 1.106 An N-terminal serine or threonine residue can be oxidized with sodium periodate to produce an aldehyde group. The reaction can be quenched with sodium sulfite to eliminate excess periodate.

Dissolve the peptide containing an N-terminal serine or threonine group at a concentration of at least 2mg/ml in 0.04 M sodium phosphate, pH 7.0. Higher concentrations of peptides or proteins may be used without modification to the rest of the protocol, because the amount of periodate used in the reaction is in sufficient molar excess, even when low-molecular-weight peptides are being oxidized. Peptides that are initially insoluble... 

Because of their neighboring amino and hydroxyl groups both serine and threonine can be oxidized with periodate to give formaldehyde or acetaldehyde, respectively. 

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