• Background
• Methods
• Results
• Discussion
• Future work

BACKGROUND
The Application of L-tert-leucine

L-tert-leucine is an important and attractive chiral building block. Owing to its bulky and hydrophobic tert-butyl side chain which would provide particularly great steric hindrance in the process of reaction, this unnatural amino acid is widely used as chiral auxiliaries and catalysts in asymmetric synthesis in developing chiral pharmaceutically active chemicals.

1.1. Asymmetric synthesis by L-tert-leucine and its derivatives

When L-tert-leucine or its derivatives were employed in asymmetric reactions, the results always showed high enantioselectivities. For example, the following reaction is a reported Michael additions of Grignard reagents to a,b-unsaturated aldimines derived from L-tert-leucine (Figure 1). After hydrolysis and hydrogenation, the finalist product shows high enantiomerical purity. Owing to the bulky tert-butyl side chain of compound 1, the side of stronger steric hindrance was locked. Grignard reagents could only attack compound 1 from the special side so that the product shows high enantiomerical purity.

1.2. Pharmaceutical applications of L-tert-leucine

L-tert-leucine can applied in various Pharmaceutical field. L-tert-leucine was introducted into new and more efficient protease inhibitors of many viral diseases, such as HIV, IL-l-induced cartilage degradation and so on.

As we can see, AIDS is an awful disease which disturbed humans for many years. Investigations show that HIV-protease is an aspartic acid protease which is necessary for viral replication. So inhibition of this protease makes HIV non-infectious. The most favorable HIV-protease inhibitors structure are phenylnorstatine [(2R,3S)-3-amino-2-hydroxy-4-phenylbutyric acid, Figure 2] and its derivatives.

In order to optimized protease inhibitors, numerous protected, deprotected and derivatized L-tert-leucines are used to modify phenylnorstatine. Modified compounds could be nice protease inhibitors with considerable antiviral activity.

For the treatment of IL-l-induced cartilage degradation in tissue culture , L-tert-leucine plays an important role. Thirty years ago, Roche company discoved an N-substituted Tle-N-methylamide (Ro 31-9790, Figure 3) to be an potent collagenase inhibitor which could prevent IL-l-induced cartilage degradation.

L-tert-leucine is essential in many fields so that the large-scale production is indispensible.

Reference

1. Takayuki Shioiri, Kunisuke Izawa, and Toshiro Konoike. Pharmaceutical Process Chemistry. WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. 2011. 184-205

2. Andreas S. Bommarius, Michael Schwarm, Klaus Stingl, Matthias Kottenhahn, Klaus Huthmacher and Karlheinz Drauz. Synthesis and Use of Enantiomerically Pure tert-Leucine.Tetrahedron: Asymmetry. 1995, 6, 2851-2888

3. P. Ettmayer, M. Hübner, A. Billich, B. Rosenwirth, H. Gstach, Bioorg. Med.Chem. Lett. 1994, 4, 2851-2856

4. D. J. Kempf, L. M. Codacovi, D. W. Norbeck, J. J. Plattner, H. Sham, S. J. Wittenberger, C. Zhao (Abbott), Patent Appl. EP 486948, 1992

5. P. A. Brown, W. H. Johnson, G. Lawton (Hoffmann-La Roche), EP Appl. 0497 192, 1992