Abstract
In this account several tools necessary for the synthesis of
peptides from α-amino acids are considered. Different strategies for
the asymmetric synthesis of α-amino acids are studied.
New chiral glycine and alanine imines as acyclic and cyclic templates
for the asymmetric synthesis of different types of mono as well
as dialkylated α-amino acids with acyclic and heterocyclic
structures are reviewed. Their diastereoselective alkylation and
final hydrolysis takes place under very mild reaction conditions.
New polymer-supported cinchonidine and cinchonine ammonium salts
and chiral binaphthol-derived aminoalkoxides (BINOLAMs), have been developed
as catalysts for the asymmetric PTC alkylation of imino esters.
The use of chiral oxazinone and pyrazinone α,β-didehydroamino
acid derivatives in hydrogenation, Heck-arylation, cyclopropanation
and Diels-Alder cycloaddition reactions for the asymmetric
synthesis of α-amino acids are also studied. Azomethine
ylides derived from saturated oxazinones can also be used in the
asymmetric synthesis of prolines by means of diastereoselective dipolar
cycloadditions. For the protection of α-amino acids new
efficient reagents, Fmoc-P-OSu and Cbz-P-OSu, derived from poly(styrene-co -N -hydroxymaleimide)
named as polymeric N -hydroxysuccinimide
(P-HOSu), have been developed. Several new systems such as polymer-supported
P-HOSu/DCC and polystyrene-bound P-TBTU or P-HBTU, together
with non- polymeric thiouronium salts derived from 2-mercaptopyridine-1-oxide
and TMU, such as HOTT and TOTT, and from DMPU, such as HODT and TODT,
have been used as peptide coupling reagents, in solution and solid
phase peptide synthesis, as well as for the preparation of primary
amides, Weinreb amides and other hydroxamates, directly from carboxylic
acids.
1 Introduction
2 Asymmetric Synthesis of α-Amino Acids
2.1 Electrophilic Alkylation of Chiral Glycine and Alanine
2.2 Electrophilic Alkylation with Chiral Phase-transfer
2.3 Chiral α,β-Didehydroamino Acid Derivatives
2.4 Chiral Azomethine Ylides
3 Protecting-group Reagents
4 Peptide Coupling Reagents
5 Conclusion
Key words
amino acids - phase-transfer catalysis - asymmetric catalysis - protecting groups - peptides
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