AMINO ACIDS, tert-BUTOXYCARBONYLATION

Ethyl or Isopropyl acetate may also be used as extraction solvents for less lipophilic N-tert-butoxycarbonyl amino acids. 

A -tert-butoxycarbonyl amino acid (a Boc-amino acid)... 

The next five procedures of the final set illustrate the important process of preparation of enantiomerically pure materials beginning with readily available enantiomerically pure natural substances. Use of commercially available enantiomerically pure pyrrolobenzodiazepine-5,11-diones to prepare (1S,2S)-(+)-2-(N-TOSYLAMINO)CYCLOHEXANECARBOXYLIC ACID is described in the first procedure. The next preparation illustrates an optimized preparation of DIETHYL (2S,3R)-2-(N-tert-BUTOXYCARBONYL)AMINO-3-HYDROXYSUCCINATE... 

The alkoxycarbonyl protecting groups can also be introduced into amines by, triazolides (Table 4—7). With A-tert-butoxycarbonyl-1,2,4-triazole the tert-butoxy-carbonyl protecting group (Boc) is transferred readily onto amino functions of primary amines, trimethylbenzyl ammonium salts of amino acids, or peptides.[ 1965 Alternatively, the Boc group can be transferred with terf-butylphenylcarbonate in the presence of 1,2,4-triazole. In this latter approach the triazolide is presumably formed as an intermediate. ... 

Scheme 2.31 Synthesis of a-allenic a-amino acid derivatives 90 by 1,6-cuprate addition. Boc = tert-butoxycarbonyl.

Furthermore, a highly efficient route to A-tert-butoxycarbonyl (Boc)-protected p-amino acids via the enantioselective addition of silyl ketene acetals to Al-Boc-aldimines catalyzed by thiourea catalyst 4 has been reported (Scheme 12.2)." From a steric and electronic standpoint, the A-Boc imine substrates used in this reaction are fundamentally different from the A-alkyl derivatives used in the Strecker reaction. 

R Synthesis of N-(tert-Butoxycarbonyl)-3-lodoalanine Methyl Ester A Useful Building Block in the Synthesis of Nonnatural a-Amino Acids via Palladium Catalyzed Cross Coupling Reactions. 

Asymmetric Synthesis of N-tert-Butoxycarbonyl a-Amino Acids Synthesis... 

The individual amino acid building blocks are first incubated with di-tert-butyl dicarbonate, thus forming a tert-butoxycarbonyl amide (BOC) amino acid derivative. 

Asymmetric Synthesis of N-tert-Butoxycarbonyl a-Amino Acids Synthesis of (5S,6R)- and (5R,6S)-4-tert-Butoxycarbonyl-2,3-diphenylmorpholin-6-one. 

Stereochemically controlled synthesis of this subunit, which contains five stereogenic centers, is important to an efficient bleomycin synthesis. (2S,3S,4i )-4-(/er/-Butoxycarbonyl-amino)-3-hydroxy-2-methylpentanoic acid (15) was obtained via a stereoselective syn aldol addition of a boron Z-enolate with (27 )-2-(tert-butoxycarbonylamino)propanal (Scheme 4). Similarly, the L-threonine subunit 18 was prepared by diastereoselective syn aldol addition of an N- acy I ox azo I i di n one stannous Z-enolate with acetaldehyde. The bithiazole unit 19 was prepared using a direct DCC-promoted condensation of 3-(methylsulfanyl)propylamine. Convergent access to tetrapeptide S was obtained by coupling of acid 15 and deprotected 18 to give dipeptide 20, followed by further coupling with the bithiazole 19 to ultimately give tetrapeptide S (21). 

The tert-butoxycarbonyl (i-BOC) group is often used for protection of the amino, hydroxy, and sulfhydryl groups. This kind of defense is usual in the protection of amino acids in peptide synthesis. 

Amino acid residues are added by beginning at the C terminus in the Merrifield solid-phase approach to peptide synthesis. Thus the synthesis of Phe-Gly requires glycine to be anchored to the solid support. Begin by protecting glycine as its tert-butoxycarbonyl (Boc) derivative. 

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