Molecular Discrimination of N-Protected Amino Acid Esters by a Self-Assembled Cylindrical Capsule:  Spectroscopic and Computational Studies

Abstract

A self-assembled, cylindrical capsule was used to bind N-alpha-protected amino acid esters. The reversible encapsulation was studied using NMR spectroscopy in deuterated mesitylene solution and by computer-aided molecular modeling. BOC-L-alanine alkyl esters and BOC-beta-alanine alkyl esters were tested as guests, and the relative binding affinities were established by direct competition experiments. A good correlation was found between the experimental and calculated relative binding affinities in these two series. Guests that were slightly longer than the internal dimensions of the cavity were accommodated by adopting compacted conformations.

High Yielding Methyl Esterification Catalyzed by Indium(III) Chloride

“…Products of entries 1-4, 6, 10, 12, 13, and 15 could be compared with the commercially available sources, and the product of entries 8, 9, and 11 was identical with those of the previously reported spectroscopic data. [12][13][14] 3- (2,4,6 …”

“…The reaction with ketopinic acid required 96 h to complete and ended up with 61% yield, presumably due to the steric hindrance (entry 11). A couple of esterification employing sonication was attempted, and we revealed that the reaction could proceed at room temperature, shortening the reaction time in half (entries [12][13][14]. We also revealed that it was possible to carry out the esterification in the presence of the water molecules, using the catalytic amount of indium(III) chloride tetrahydrate instead of indium(III) chloride, without affecting the completion of the esterification (entry 15).…”

‘Naked‐eye’ enantioselective chemosensors for N‐protected amino acid anions bearing thiourea units

“…[1][2][3] Amino acids and their derivatives are important components of chemical and biological systems, and their recognition, in particular, chiral recognition attracts considerable interest. [4][5][6][7] Various approaches involve the use of metal complexes, 8,9 imprinted polymers, 10,11 natural and modified cyclodextrins, [12][13][14] synthetic macrocycles (including calixarenes), [15][16][17] and different types of acyclic compounds [18][19][20] as host molecules. Often a chiral host is prepared by using a natural chiral compound as precursor or modifier.…”

Self-fulfilling cavitands: Packing alkyl chains into small spaces

“…The recent literature describes several systems in which the energetic preference for the anti conformation may be overcome by imposing geometric constraints on the size and shape of the space available (3)(4)(5)(6)(7)(8)(9)(10)(11). Naturally occurring protein receptors (12) and synthetic host molecules contain binding cavities suitable for hydrocarbons, and a variety of conformations have been observed by crystallography in the former and NMR in the latter.…”

“…Normal alkanes are simply flexible and adept at filling spaces of diverse shape. We have examined normal alkanes in several hosts: hexameric pyrogallolarene assemblies encompassing a roughly cube-like space of Ϸ1,300 Å 3 (11); vase-shaped, water-soluble cavitands having an open-ended pocket of Ϸ200 Å 3 (7,8); and a cylindrical molecular capsule having an inner space of 425 Å 3 (6,9). The behavior in these systems fits neither Fischer's (13) lock-and-key model nor the Thoma and Koshland (14) induced-fit model: the alkane contorts to be accommodated; it assumes the size, shape, and chemical surface that are proper to the space on offer in the receptor.…”