A General Method for High-Pressure-Promoted Postfunctionalization of Unclosed Cryptands: Potential Phase-Transfer Catalysts

Anion Recognition by a Pincer-Type Host Constructed from Two Polyamide Macrocyclic Frameworks Jointed by a Photo-Addressable Azobenzene Switch

A sterically crowded light-responsive host 1 was synthetized with a 93% yield by applying a post-functionalization protocol utilizing the double amidation of 4,4'-azodibenzoyl dichloride with a readily available 26-membered macrocyclic amine. X-ray structures of two hydrates of trans-1 demonstrate a very different alignment of the azobenzene linkage, which is involved in T-shape or parallel-displaced π⋯π stacking interactions with the pyridine-2,6-dicarboxamide moieties from the macrocyclic backbone. Despite the rigidity of the macrocyclic framework, which generates a large steric hindrance around the azobenzene chromophore, the host 1 retains the ability to undergo a reversible cis⟷trans isomerization upon irradiation with UVA (368 nm) and blue (410 nm) light. Moreover, thermal cis→trans back-isomerization (ΔG0 = 106.5 kJ∙mol-1, t½ = 141 h) is markedly slowed down as compared to the non-macrocyclic analog. 1H NMR titration experiments in DMSO-d6/0.5% water solution reveal that trans-1 exhibits a strong preference for dihydrogenphosphate (H2PO4-) over other anions (Cl-, MeCO2-, and PhCO2-), whereas the photogenerated metastable cis-1 shows lower affinity for the H2PO4- anion.

Stabilization of Near Identical Hydrogen Bonded Octameric Water Clusters in Crystal Structures of Three Distinct Non-Charged Polyamide Macrocyclic Host Molecules

In this paper, we present a comparative analysis of the solid state structures of three well-resolved hydrates of macrocyclic host molecules 1a, 1b, and 2 containing an intrannular amide-aryl substituent (lariat arm) connected to a fixed 26-membered ring in a normal (-NHCOAr, hosts 1a and 1b) or reverse manner (-CONHAr, host 2). Despite different chemical structures, these hosts crystallize as isostructural tetrahydrates in the same P-1 space group. Moreover, their crystals exhibit identical hydrogen bond motifs resulting in a stabilization of an almost identical unusual octameric water cluster built from the cyclic tetramer core and four water molecules, attached sequentially in an "up-and-down" manner. Further analysis reveals that, among the series, the structure of host 2 provides the most suitable environment for the accommodation of this type of water cluster.

Divergent synthesis of pyrrolidine and glutamic acid derivatives using a macrocyclic phase-transfer catalyst under high-pressure conditions

The reactivity of the glycine ketimine ester with α,β-unsaturated ketones in the presence of macrocyclic hybrid phase-transfer catalysts under high pressure conditions has been investigated.

Tuning Anion-Binding Properties of 22-Membered Unclosed Cryptands by Structural Modification of the Lariat Arm

A series of 22-membered unclosed cryptands end-capped with intra-annular methyl (1), phenyl (2), p-tert-butylphenyl (3), and p-nitrophenyl (4) amide substituents (lariat arm) were synthesized to elucidate the effect of steric and electronic factors on their anion recognition behavior. The ¹H NMR titrations in DMSO-d ₆ with 0.5% water reveal enhanced selectivity for H₂PO₄ ^- vs Cl^- and PhCO₂ ^-. The para-attachment of the electron-withdrawing nitro group (-NO₂ vs -H and -t-Bu) was found to increase anion-binding affinity, whereas the steric bulkiness of lariat arm (methyl vs aryl) has a marginal effect. DFT calculations reveal that binding of H₂PO₄ ^- is associated with minimal conformational change in the lariat arm moiety and involve four hydrogen bond acceptor and one donor sites of host.

Static Combinatorial Chemistry: A High-Pressure Approach to the Synthesis of Macrocyclic Benzoamide Libraries

We investigated the yield and distribution of macrocyclic products formed in combinatorial libraries (CLs) obtained via double-amidation reactions of methyl diesters with α,ω-diamines. The application of the static combinatorial chemistry (SCC) approach allowed us to generate a large number of macrocyclic diamides and tetraamides in single experiments. We show that high-pressure conditions accelerate the macrocyclization process but also have a great impact on the distribution of macrocyclic products in the presented libraries, promoting the formation of macrocyclic compounds and eliminating the linear ones. The distribution of macrocyclic products was also found to be strongly dependent on the structural features of the substrates employed. Furthermore, in three- and four-substrate CLs we observed the formation of a new type of hybrid tetraamides consisting of three different components.