Dimerization of Glycine Derivatives

Abstract

The bromide (5), prepared by treatment of the glycine derivative (4) with N-bromosuccinimide, reacted with hexabutylditin to give diastereoisomers of the glycine dimer (7), only when moisture was rigorously excluded from the reaction. Otherwise the major products were the diastereoisomers of the ether (11). The structure of the racemic diastereoisomer (11) was determined by X-ray crystallography. Photolysis of mixtures of the glycine derivative (4) and di-t-butyl peroxide gave the alanine derivative (10) in addition to the diastereoisomeric dimers (7).

β-Nitro-α-amino acids as latent α,β-dehydro-α-amino acid residues in solid-phase peptide synthesis

“…The decreased reactivity in this system can be attributed to the increased steric constraints associated with bringing the substituents at the α-and β-positions into coplanarity, during the change in hybridization. 6 By analogy, loss of nitrous acid from β-nitroalanine derivatives is more facile 6 and this may be occurring during the use of the amino acid 7a in peptide synthesis, leading to decomposition of reactive dehydroalanine derivatives and the failure to produce the peptide 15. However, since dehydroalanine derivatives are readily prepared from serine, they are already accessible by methods that are truly complementary to the approach presented here.…”

“…1 Free dehydro amino acids are generally unsuitable for direct peptide synthesis because developing a complementary approach involving the incorporation of β-nitro-α-amino acids in peptides as latent α,β-dehydro-α-amino acid residues. β-Nitro amino acids with a wide variety of side chains are easily prepared through reaction of α-bromoglycine derivatives with alkyl nitronates 6,7 or, more directly, through the three-component coupling of amines, nitroalkanes and glyoxylate in aqueous base. 8 Previously we have shown that the amino acid tert-butyl esters can be incorporated as the C-terminal residues in N-and C-protected dipeptides, using solution-phase methods.…”

Exploration of Dimethylzinc‐Mediated Radical Reactions

“…It is a plausible explanation that triethylborane activates N-alkoxycarbonyl imines bearing an electron-donating aromatic ring by complexation, but does not activate N-Ts imines. However, we have not yet succeeded in observing an indication of this complexation in either 1 H, 13 C, or 11 B NMR studies of the mixture of 1f and triethylborane. [70][71][72] N-Alkoxycarbonyl imines also showed their quality as good radical acceptors in the addition reactions of imidomethyl radicals.…”

“…[40] Therefore, it would be reasonable to assume that the mechanism is as shown in Eqs. (13) to (15)…”

Modifications of Amino Acids and Peptides via Radicals

“…Other side-chain functional groups may also be manipulated to produce amino acid radicals [8,[54][55][56][57][58], and, in particular, Barton decarboxylation of aspartate and glutamate derivatives has been applied in this manner (Scheme 8) [55]. Related procedures have been developed to generate amino acid radicals by dehydroxylation of hydroxy amino acid derivatives [56].…”