Versatility of b-lactams in synthesis.
Studies directed toward the synthesis of complex nucleoside antibiotics
and some macrocyclic peptides*
Claudio Palomo**, Jesús M. Aizpurua, Iñaki
Ganboa, and Mikel Oiarbide
Departamento de Química Orgánica, Facultad
de Química, Universidad del País Vasco, Apdo 1072, 20080
San Sebastián, Spain
Abstract: The diastereoselective [2+2] cycloaddition of a-hydroxyketene
equivalents with chiral a,w-oxyaldehyde-derived
imines followed by the 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-promoted
ring expansion of the resulting a-hydroxy
b-lactam adducts provides an unconventional
and short route to a-amino acid N-carboxy
anhydrides (NCAs). The required enantiopure a,w-oxyaldehydes
were obtained either from the chiral pool or through the Sharpless AD
methodology. Following the present strategy, several nonproteinogenic
NCAs were synthesized, which were further coupled with a-amino
acid esters giving rise to key fragments of some nucleoside antibiotics
and macrocyclic peptides.
*Lecture presented at the 13th International
Conference on Organic Synthesis (ICOS-13), Warsaw, Poland, 1-5 July
2000.
** Corresponding author
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