Leucine revised

Revision Classifications and reactions added for a-Acetolactatedecarboxylase Aminopeptidase, Leucine and Lysozyme Heavy Metals (as Pb) specification and determination deleted from Additional Requirements. 

The circulins—As early as 1949, Peterson and Reineke characterized circulin as its sulphate. Total hydrolysis yielded D-leucine, L-threonine and L-K,y-diaminobutyric acid together with an optically active isomer of pelargonic acid. The existence of two components, found by Peterson and Reineke was later confirmed by the chromatographic separation of crude circulin into two major components, named circulin A and circulin B. In addition there was evidence for at least three other ninhydrin-positive, biologically active entities. In the hydrolysate of circulin A, L-isoleucine was found besides the amino acids previously reported . Quantitative amino acid analysis showed circulin A and B to be composed of L-a,y-diamino-butyric acid, L-threonine, D-leucine, L-isoleucine and ( + )-6-methyloctanoic acid in the molar ratio 6 2 1 1 1. After partial acid hydrolysis, fractionation and structure determination of the resulting peptides, circulin A and circulin B were formulated as cyclodecapeptides . Very recently, however, Japanese workers have revised the structure of circulin A. According to them, circulin A differs from colistin A only by a replacement of L-leucine in the latter by L-isoleucine Figure 1.7). 

In 2010, de Lera et al. synthesized the heterodimeric diketopiperazine (+)-pestalazine B (658) (416). With this material in hand, they were able to revise the earlier proposed structure 659 for the natural product. These investigators utilized a convergent synthesis strategy, starting with the condensation of L-trypto-phan methyl ester (616) and IV-Fmoc-o-phenylalanine (652), to give diketopiperazine derivative 653 after Fmoc-deprotection (Scheme 10.6). This was reacted with 3a-bromopyrrolidinoindoline 654 (417) to furnish the dimeric product 655. Boc-deprotection ( 656), coupling with iV-Fmoc-o-leucine ( 657), and Fmoc-deprotection finally led to compotmd 658 for which the spectroscopic data matched those of the natural product. 

Esperinic acid was studied by mass spectrometry and the revised structure (42) was established (705), in which 30% of the C-terminal l-leucine was replaced by L-valine. In order to locate the lactone ring esperin was treated with hydrazine followed by Curtius rearrangement... 

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