HOST-GUEST COMPLEXATION .20. CHIRAL RECOGNITION IN TRANSPORT AS A MOLECULAR-BASIS FOR A CATALYTIC RESOLVING MACHINE

Enantiomer differentiation (chiral recognition) occurred when designed, chiral hosts complexed and carried racemic amine salt guests from one aqueous solution through chloroform to a second aqueous solution where the guests were released. Optically pure hosts examined were 22-membered ring systems containing six roughly coplanar ether oxygens regularly spaced by attachment to one another through four ethylene (E) units. Two 1, 1ʹ-dinaphthyl (D) units of identical configuration, attached to oxygens at their 2, 2ʹ positions, provided chiral barriers in the cycles. Besides the parent host, D(OEOEO)2D (1), two others were examined in which one of the dinaphthyl units was substituted in its 3, 3ʹ positions to give (CH3)2D(OEOEO)2D (2) and (ClCH2)2D(OEOEO)2D (3). Chloroform solutions of these hosts (0.027 M), stirred at 24 °C in the bottom of a U-tube, contacted aqueous layers in the two arms. The solution in the α arm was 0.80 M in LiPF6, 0.08 M in HCI, and 0.05-0.28 M in guest *RNH3C1 or *RNH3Br salt. The aqueous solution in the β arm was 0.10 M in HCI. Guests examined were C6H5CH(CH3)NH3Br (4), C6H5CH(C02CH3)NH3C1 (5), and p-H0C6H4(CO2CH3)NH3Cl (6). Rate constants for transport were measured for the faster moving A enantiomer (kA*) and the slower moving B enantiomer (kB*). Values of kA*/kB* varied from 1.45 (host 1 and guest 4) to 10 (host 2 and guest 5) and correlated roughly with DADB values, where DA was the distribution coefficient of the more and DB that of the less complexed enantiomer drawn from the aqueous into chloroform phases in one-plate extraction experiments. Hosts 2 and 3, with their chiral barriers extended with CH3 or CICH2 substituents, and the amino ester guests (5 and 6) gave the greatest chiral recognition in transport. The direction of the configurational bias in complexation corresponded to expectations based on scale molecular model examination of the diastereomeric complexes. A W-tube was designed for continuous and simultaneous removal of each enantiomer of racemic 5 from a central aqueous solution contacting two separate chloroform pools, one containing (S.S)- 2 and the second (R, R)-2. The enantiomeric guests were delivered to separate aqueous solutions, one in the left-and the other in the right-hand arm of the W-tube. Depending on experimental details, the S, S host delivered L-5 to the left-hand aqueous pool in optical purities that ranged from 70 to 86%, and the R, R host delivered D-5 to the right-hand aqueous pool in optical purities that ranged from 77 to 90%. © 1979, American Chemical Society. All rights reserved.