Biosynthesis of Pyrrolidine Alkaloids

Simple Pyrrolidine Alkaloids.—It is well established that ornithine (1) is a key precursor in the biosynthesis of pyrrolidine alkaloids. Notably, the amino-acid (1) is utilized for the biosynthesis of nicotine (5) via the symmetrical intermediate putrescine (3), whereas the biosynthesis of tropane alkaloids, e.g. scopolamine (6), avoids any symmetrical intermediate1,2 (cf. Vol. 11. p. 1). 

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. 

---