Pyrrolines, deamination

A -Pyrroline has been prepared in low yield by oxidation of proline with sodium hypochlorite (71), persulfate (102), and periodate (103). A -Pyrroline and A -piperideine are products of enzymic oxidation via deamination of putrescine and cadaverine or ornithine and lysine, respectively (104,105). This process plays an important part in metabolism and in the biosynthesis of various heterocyclic compounds, especially of alkaloids. 

Lemal and McGregor showed that such ring openings are stereospecific and may be rationalized by the use of molecular correlation diagrams e.g. trans-2,5-dimethyl-3-pyrroline is deaminated by this procedure to pure cis, trans-2,A-hsm-diene and cw-2,5-dimethyl-3-pyrroline to the pure irons, irons isomer, viz. 

Another very simple approach to 18,20-oxygenated steroids is nitrous acid deamination of pyrrolines of the type CCXXXVI. In this manner, Buzetti et al. 165) prepared 18-hydroxyprogesterone CCXXXII. The pyrrolines (CCXXXVI) are readily accessible from the demethyl-conanine type (CCXXXIV) by the Ruschig method. The position of the double bond was established 98) in a model pyrroline from the absence... 

The presence of some enamine, at equilibrium, is demonstrated by the conversion of piperideine into a dimer, indeed, the ability of these two systems to serve as both imines and enamines in such condensations is at the basis of their roles in alkaloid biosynthesis. Formed in nature by the oxidative deamination and decarboxylation of ornithine and lysine, they become incorporated into alkaloid structures by condensation with other precursor units. Hygrine is a simple example in which the pyrroline has condensed with ace-toacetate, or its equivalent. 

The coupling of 3-pyrrolin-3-yl triflates with arylboronic acids leads to 3-arylpyrroles because of concurrent dehydrogenation. A caveat of the coupling involving haloanilines is that deamination also occurs to some extent. 

The potential of biotransformations with genetically modified microorganisms can be illustrated by the following example, where the chain of added-value to amino acid products is also recognisable The Mercian Company (Japan) uses a recombinant E. coli strain to prepare (S)-piperidine-2-car-boxylic acid from (L)-lysine. In this strain, the (L)-lysine-permease transport system is overexpressed, so that in this pathway lysine is produced efficiently in the cells. The bacteria possess additionally a (L)-lysine-aminotransferase from Flavobacterium lutescens, which brings about the deamination of lysine. The thus generated aldehyde is in equilibrium with its intramolecular imine, which, in presence of the E. co/i-specific pyrroline-5-carboxylate reductase, is reduced with NADPH to (S)-piperidine-2-carboxylic acid. The turnover... 

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