Barricyclin D1—a dimeric ellagitannin with a macrocyclic structure—and accompanying tannins from Barringtonia racemosa

Our examination of high molecular weight polyphenolic constituents in the leaves of Barringtonia racemosa of the family Lecythidaceae uncovered five previously undescribed ellagitannins. One, barringtin M1 (1), among them was a hydrolysable tannin monomer, while remaining four, barringtins D1 (2), D2 (3), D3 (4) and barricyclin D1 (5), were all dimers. Barricyclin D1 had a first macrocyclic structure formed from casuarictin (6) and tellimagrandin I (7), and the other ellagitannins had structures related to 5. Two additional known phenolics, valoneic acid dilactone (8) and schimawalin A (9), were also isolated from the leaves. These results suggested that the leaves of B. racemosa is a natural resource rich in hydrolysable tannin oligomers.

A fluorescent calix[4]arene with naphthalene units at the upper rim exhibits long fluorescence emission lifetime without fluorescence quenching

Macrocyclic structure brings long fluorescence lifetime emission without fluorescence quenching and TD-DFT calculations revealed π–π interactions between the naphthalene rings.

Impact of the macrocyclic structure and dynamic solvent effect on the reactivity of a localised singlet diradicaloid with π-single bonding character

An extremely long-lived localised singlet diradical with π-single bonding character is found in a macrocyclic structure that retards the radical–radical coupling reaction by the “stretch and solvent-dynamic effects”.

Synthesis and structural characterization of dialkyltin complexes of N-salicylidene-L-valine

The synthesis and characterization of five new chiral dialkyltin complexes of N-salicylidene-L-valine, [2-O-3-R-5-R'C6H2C(H)=NCH(CH(CH3)2)C(O)O]SnR''2 (R, R', R'' = H, H, Me (1); H, Br, Me (2); OMe, H, Et (3); Br, Br, n-Bu (4); CH(OMe)2, Me, n-Bu (5)), have been reported. Compounds 1-5 are all (S)-enantiomers, and their crystal structures have been studied. Compound 1 displays a trimeric macrocyclic structure in which the coordination environment of each tin atom is a distorted [SnC2NO3] octahedron. In complexes 2-5, the tin atom has an intermediate geometry between trigonal bipyramidal and square pyramidal, and 3 is closer to a square pyramid. In crystals, a zigzag supramolecular chain is formed by the intermolecular C-H…O, O-H…O or Sn…O interactions.

Ru(II)Porphyrinate-Based Molecular Nanoreactor with Unusual Coordinative Properties and Extraordinary Chemical Selectivity in N–H Bond Carbene Insertion Reactions

A 5,15-bis(1,1’-biphenyl)porphyrin-based molecular clip covalently-linked to a stiff phenanthrene appended moiety yields a porphyrin-based macrocycle with a well-defined and relatively small cavity in the solid-state and in solution. Introduction of a Ru(II) ion into the porphyrin moiety followed by axial coordination of the inert and bulky diphenylcarbene ligand exo-to the macrocycle’s cavity affords a Ru(II)porphyrinate-based macrocycle able to promote the active-metal template [2]rotaxane synthesis in quantitative yield through the challenging single N–H bond carbenoid insertion. A detailed structural investigation of the Ru(II)porphyrinate-based macrocycle and the resulting asymmetrical [2]rotaxanes reveals that the synergy between the steric shielding provided by the hollow macrocyclic structure and the kinetic stabilization of otherwise labile coordinative bonds, warranted by the mechanical bond, can be used as principles for the design of molecular nanoreactors.

Ru(II)Porphyrinate-Based Molecular Nanoreactor with Unusual Coordinative Properties and Extraordinary Chemical Selectivity in N–H Bond Carbene Insertion Reactions

A 5,15-bis(1,1’-biphenyl)porphyrin-based molecular clip covalently-linked to a stiff phenanthrene appended moiety yields a porphyrin-based macrocycle with a well-defined and relatively small cavity in the solid-state and in solution. Introduction of a Ru(II) ion into the porphyrin moiety followed by axial coordination of the inert and bulky diphenylcarbene ligand exo-to the macrocycle’s cavity affords a Ru(II)porphyrinate-based macrocycle able to promote the active-metal template [2]rotaxane synthesis in quantitative yield through the challenging single N–H bond carbenoid insertion. A detailed structural investigation of the Ru(II)porphyrinate-based macrocycle and the resulting asymmetrical [2]rotaxanes reveals that the synergy between the steric shielding provided by the hollow macrocyclic structure and the kinetic stabilization of otherwise labile coordinative bonds, warranted by the mechanical bond, can be used as principles for the design of molecular nanoreactors.

Two-stage threecomponent synthesis of 6,11-diaza-1,5(2,5)-dioxazole- 3(1,2)-benzenecycloundecapha ne-14,54- dicarbonitrile

The possibilities of 2-amino-3,3-dichloroacrylonitrile (ADAN) used for the construction of macrocyclic structures such as cyclophanes with two oxazole fragments are investigated. For this purpose, bifunctional reagents were used in the classic ADAN transformation into 5-amino-4-cyanooxazoles (sequential treatment of ADAN with acyl chloride and a primary or secondary amine). As a result of the reaction of 2,2'‎-(1,2-phenylene)-diacetyl chloride with 2 eq of ADAN, a compound with two acrylonitrile fragments, 2,2' ‎- (1,2-phenylene)bis(N- (2,2-dichloro-1-cyanovinyl)acetamide), was obtained. In this substance, both ADAN residues can interact with amines and form oxazole cycles: for example, the treatment with an excess of dimethylamine produces 2,2'‎ - (1,2-phenylenebis(methylene))bis(5-(dimethylamino)oxazole-4-carbonitrile). The target macrocyclic structure was obtained by the interaction of 2,2'‎ - (1,2-phenylene)bis(N-(2,2-dichloro-1-cyanovinyl)acetamide) with butane-1,4-diamine, as a result the simultaneous forming of both oxazole rings and an aliphatic bridge connected with them was happened. At this stage, it was used a procedure, that is typical of the creation of macrocyclic structures based on polyfunctional reagents, — strong dilution (about 0.04 M). The molecule of the synthesized 6,11-diaza-1,5(2,5)-dioxazole-3(1,2)-benzenecycloundecaphan-14,54-dicarbonitrile has high spatial symmetry, which is confirmed by the presence of only one series of peaks in the 1H and 13C NMR spectra (for example, the butane-1,4-diamine fragment in the aliphatic part of the spectrum looks likes two triplets). The formation of a macrocyclic structure is evidenced by HPLC-MS data, as well as homo- and heteronuclear correlations in the NMR spectra. The proposed procedure for the synthesis of 6,11-diaza-1,5(2,5)-dioxazole-3(1,2)-benzenecycloundecaphan- 14,54-dicarbonitrile is based on the use of simple and inexpensive reagents, and the total yield of the target substance in two stages starting with the 2,2'‎ - (1,2-phenylene)diacetyl chloride, is 51 %.

Crown Procyanidin Tetramer: A Procyanidin with an Unusual Cyclic Skeleton with a Potent Protective Effect against Amyloid-β-Induced Toxicity

The structure of a new procyanidin tetramer, which we call a crown procyanidin tetramer, with an unprecedented macrocyclic structure has been characterized for the first time. Its comprehensive spectroscopic analysis revealed that it is a symmetric procyanidin tetramer composed of four (−)-epicatechin sub-units linked alternatively via 4β→8 or 4β→6 B-type interflavanyl linkages to form the macrocyclic structure. This NMR-characterized carbon skeleton has never been reported before for procyanidins in grape or in wine, neither in the plant kingdom. Surprisingly, the crown procyanidin tetramer appeared to be specifically localized in grape skin, contrasting with the oligomeric and polymeric procyanidins present in seed, skin, and bunch stem. Moreover, this crown procyanidin tetramer showed promising protective effects against amyloid-β induced toxicity.