Chelating from amino acids, synthesizing

Typical syntheses of Co(III)-amino acid, amino acid ester, and dipeptide ester chelates are described below. The NMR spectra of the isolated products were in accord with expectation. The procedures given here are generally applicable, except for that given for [Co(en)2((iS)-GluOBzl)]I2. If this method is used to coordinate amino acids that are only partially soluble in Me2SO, more forcing conditions (extended reaction times, 1-5 h, 50-60°C) may be required. Dipeptide ester complexes are not always as amenable as [Co(en)2 (Val-GlyOEt)]I3 to crystallization from water. 

Shortly after that, Kagan and Dang made an important contribution. They synthesized the chiral diphosphine 2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane (DIOP, Figure 11b), derived from tartaric acid, and demonstrated, for the first time, the efficiency of chelating diphosphines with the asymmetry in the side chain, for the catalytic hydrogenation of amino acid precursors. 

Phenolic Mannich bases 526 and Mannich bases derived from hydrogen cyanide, precursors of a-amino acids 527 such as EDTA and similar derivatives,- - are largely used. The P-Mannich bases 528 may be also inserted into polymeric structures. - Structures represented by y-piperidone 529 and Mannich bases derived from phosphine (530) enable us to point out the wide possibility of synthesizing products having the chelating groups most suitably located for the best performance. 

The unusual amino-acid avenic acid (195), which possesses iron chelating activity has been synthesized from L-a-hydroxy-y-butyrolactone by two independent groups. Stimulated by its value in biosynthetic studies a route to chiral methylvaline has been developed based on an unusual specificity in the hydrogenation of an isopropenyl function using Wilkinson s catalyst. [3- H]Valine has also been prepared for the same purpose. 

---