Strecker ornithine

Over 500 different a-amino acids have now been synthesized or isolated. About 20 of them form the main components of proteins (see also Chapter 30). a-Amino acids are commerically obtained by fermentation of glucose (arg, asp, gin, glu, his, ile, lys, pro, val, thr) or glycine (ser), or enzymatic attack on aspartic acid (ala) or fumaric acid (asp), by hydrolysis, for example, of casein or sugar beet waste (arg, cys, his, hyp, leu, tyr), by transformation of ornithine (arg) or glutamic acid (gin), or, alternatively, by complete synthesis from aldehydes using the Strecker synthesis (ala, gly, leu, met, phe, thr, trp, val), from acrylonitrile (gly, lys), or from caprolactam (lys). The racemates are obtained by total synthesis, but L-amino acids are produced by all the other processes. The racemates are separated and the D-isomers produced are again racemized. 

Strecker degradation of both proline (cf. Formula 5.14) and ornithine (cf. Formula 5.15). 

The Strecker degradation of ornithine proceeds analogously, but the intermediate 4-aminobutanal forms by cychsation the final product, 1-pyrroHne (Figure 2.59). This reaction is important for the development of the characteristic aroma of bread crust (see Section 8.2.12.4.1), the aroma of other cereal products, certain fragrant rice varieties (such as Basmati rice) and in the biosynthesis of pyrrolidine alkaloids in plants (see Section 10.3.2.1.1). It was proposed that pyrrolidine and l-pyrrohne also result upon Strecker-type reaction of proline by a-dicarbonyl compounds. 

Figure 2.59 Strecker degradation of ornithine by a-dicarbonyi compounds.

Smith, A.D., M. Benziman, andH.J. Strecker, 1967. The formation of ornithine from proline in animal tissues. Biochem. J. 104, 557-563. 

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