Palladium(0)-catalyzed regioselective synthesis of alpha-dehydro-beta-amino esters from amines and allyl acetates: synthesis of a alpha-dehydro-beta-amino acid derived cyclic peptide as a constrained beta-turn mimic.
Acetates derived from the adducts of the Baylis-Hillman reaction can be reacted in a regioselective manner with amines in the presence of palladium(0) catalyst to afford alpha-dehydro-beta-amino esters (2 and 3) in good yields. The regioselectivity of the reaction can be controlled by temperature and reaction medium leading to the synthesis of regioisomers 2 or 3. The alpha-dehydro-beta-amino acid 3 is a turn inducer, and the dipeptides 6 derived from it show the presence of an eight-membered intramolecular hydrogen bond. Also, cobalt(II) chloride catalyzes the cleavage of epoxy peptides with alpha-dehydro-beta-amino acid derivative 3b to afford the corresponding dipeptide derivatives 8, which exhibit an intramolecular hydrogen bond and thus mimic a beta-turn. This intramolecular hydrogen bonding preorganizes the corresponding diallylated peptide 8c for cyclization via ring-closing metathesis to afford the cyclic peptide 9 as a constrained mimic of a beta-turn.
Rajesh
S
S
Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India.
Banerji
Biswadip
B
Iqbal
Javed
J
D000085:Acetates / Q000737:chemistry*; D000586:Amination; D000588:Amines / Q000737:chemistry*; D000596:Amino Acids / Q000737:chemistry; D002384:Catalysis; D004952:Esters / Q000138:chemical synthesis* / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D015394:Molecular Structure; D010165:Palladium / Q000737:chemistry*; D010455:Peptides / Q000138:chemical synthesis* / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature
D000085:Acetates; D000588:Amines; D000596:Amino Acids; D004952:Esters; D010455:Peptides; D010165:Palladium