Methods of Non-a-Amino Acid Synthesis, 2nd Edition

61Cyclic Precursors

2.4.4 FRom uRacil deRivatives and cyclic caRbamates

Uracil derivatives contain both an amine and a carboxyl group in the structure, and

they are effective β-amino acid surrogates. An initial cyclization reaction of the

alkene moiety of a conjugated acid such as 4-methyl-2-pentenoic acid with urea gave

dihydrouracil derivative 139.

96

Acid hydrolysis led to cleavage of the ring and forma-

tion of 4-methyl-3-aminopentanoic acid, 140. Substituted dihydrouracils have been

converted to 2-alkyl, 2,3-dialkyl, 3-alkyl, 3,3-dialkyl, and 2,3,3-trialkyl-3-amino-

propanoic acid derivatives.

97

CO

2

H

CO

2

H

NH

2

NN

O

H

H

O

H

2

N

O

NH

2

210°C

aq. HCl

heat

1391 ...