J . Am. Chem. SOC.1990, I 12, 6 144-6 145
6144
Molecular Recognition. Asymmetric Complexation of Diketopiperazines
Table 1. Binding of Diketopiperazines
entry
K . 4 . Jeong, A. V. Muehldorf, and J. Rebek, Jr.* Department of Chemistry Massachusetts Institute of Technology Cambridge, Massachusetts 02139
Synthetic receptors for neutral biochemical targets are of current interest in molecular recognition.' We describe here structures featuring convergent imide and lactam functions within cleft-like shapes; they show unusually high enantioselectivity (AAG > 2.5 kcal/mol) in their complexation of asymmetric diketopiperazines. The structures were prepared (Scheme I ) as described for Kemp's2 triacid 2a. Alkylation of hexahydrotrimesic esters followed by hydrogenation and then hydrolysis of Ib afforded the new, highly soluble propyl3 derivatives 2b (>SO% overall). Condensation with urea and activation (SOCIJ gave the acid chloride 3. Coupling to suitable diamines4 led to the diimide
Scheme I
2) R-X
R
E
3
I 2 3 4 5 6
4s 4b 4b 5 5 5
7
8 (meso) 8 (meso)
8
Received March 19, I990
host
9
10 1I 12 13 14
7a 78 7a 7b 7b 7b
equiv of 9 dissolved
titratn guest
