Synthesis of external β-turn templates by reaction of protected dehydroamino acids with cyclic enaminoesters

• Published in: Tetrahedron Vol. 61; no. 1; pp. 287 - 299
• Main Authors: Berry, Jane M., Doyle, Paul M., Young, Douglas W.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 03-01-2005
• Subjects: Annelation; GLDV-tetrapeptide; β-Turn templates; β-Turn templates; Annelation; GLDV-tetrapeptide
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2004.09.036

Two external β-turn templates have been synthesised and one of them has been derivatised as a GLDV-tetrapeptide. In the course of the synthesis an interesting dichotomy was observed in the condensation of exocyclic enamines such as
4
and
19
with protected dehydroamino acids using phosphorus trichloride. When dehydroamido acids were condensed with the enamines
4
and
19
then 6/6 and 6/5 fused bicyclic compounds such as
5
and
20
, respectively, were obtained, whereas, when dehydroamino acid urethanes were used, the 5/6 and 5/5 fused products
7
and
23
were obtained. The bicyclic template
20
was converted to the GLDV-tetrapeptide derivative
31
but the sensitivity to base of the acyl–enamine system of the template reduced the yield in the synthesis of the external turn
35
.
Graphical Abstract