A synthetic receptor for the Cbz-L-Ala-L-Ala-OH dipeptide sequence

Enantioselective binding of dipeptides using acyclic receptors

“…In contrast, the binding of N-Cbz-D-Ala-D-AlaOH by 5 leads to significant shifts of several CH as well as NH signals throughout the spectrum (although there is little overall shift to the amidopyridine NH 4 ) suggesting a much more dramatic conformational change for the receptor on binding this guest 12 and that binding of this guest is sufficiently strong to overcome the penalty of unfolding the receptor. In any event such high enantioselectivity, > 20+1 (effectively discriminating between methyl groups and hydrogen atoms), has rarely been observed in synthetic receptors, 1,10 and is particularly noteworthy in such a structurally simple acyclic receptor, which appears to lack much, if any, preorganisation for binding. Unless otherwise stated errors for K ass estimated as < 10%.…”

“…Thus receptor 4 does appear to bind dipeptides and simple amino acid derivatives, but the absolute binding constants are rather low in comparison to other diamidopyridine based receptors, and the shifts of the various NH signals on binding are also rather small in comparison to those seen in other related receptor systems. 1b, 10,11 We therefore studied receptor 5, reasoning that with additional binding functionality in the longer sidearms it might show increased affinity for peptide guests. In practice, receptor 5 initially gave absolute binding constants somewhat lower than 4 (Table 1) and again only small shifts were observed for the various NH signals on addition of guest.…”

Synthesis and binding properties of a macrobicyclic receptor for N-protected peptides with a carboxylic acid terminus

“…Furthermore, for the related macrobicyclic structure 22, incorporating an identical biaryl rim portion, the carboxamide proton resonates at 6.42 ppm in CDCl 3 solution. 13 This strongly suggests that for macrobicycle 3 there is an intramolecular hydrogen bond to NH 5 , and this is borne out by the molecular modelling results for 3 (vide infra) which showed structures in which a consistent feature was the presence of intramolecular hydrogen bonds, particularly from NH 5 to C᎐ ᎐ O 4 . In the case of macrobicycle 22, such an intramolecular hydrogen bond is not possible with the rigid aromatic ring, which links the biaryl rim to the diamidopyridine unit.…”

Recent Developments in Chiral Polynitrogenated Synthetic Receptors for Anions

“…12). Based on previous reported data [51], macrobicyclic receptor (38) was designed and synthesized, although in moderate overall yield and after many reaction steps [52]. This compound showed to be an effective receptor for dipeptides with a carboxylic acid terminus in CDCl 3 , showing selectivity for N-Cbz--alanyl-L-Xxx-OH dipeptides.…”