Synthesis and Characterisation of Macrocyclic Diamino Chiral Crown Ethers
A benign and efficient synthesis of chiral macrocyclic ‘aza-crown’ ethers of varying ring size is reported. The synthesis involves a Schiff base condensation of ether linked dialdehydes of varying chain length and (1R,2R)-(–)-1,2-diaminocyclohexane under mild conditions to yield the macrocycles, which are subsequently reduced to yield the diamino analogues.
Recognition of nitrate by the ammonium derivative of a 20-membered dioxadiaza-calix[4]arene analog—solution and solid-state study of the anion binding properties
Abstract A 20-membered dioxadiaza-calix[4]arene analog ( 1 ) was combined with a series of inorganic acids to explore the anion-inclusion properties of the corresponding ammonium dication [ 1-H 2 ] 2+ . The neutral calix[4]arene analog  1 and six salts of the receptor in the mono- or diprotonated form, [ 1-H 2 ]Cl 2 ( 2 ), [ 1-H 2 ]Br 2 ( 3 ), [ 1-H 2 ][MeOSO 3 ] 2 ( 4 ), [ 1-H 2 ][NO 3 ] 2 ( 5 ), [ 1-H 2 ][ClO 4 ] 2 ( 6 ), and [ 1-H ][ClO 4 ] ( 6b ), were structurally characterized by single-crystal X-ray diffraction analysis, which enabled a detailed comparative analysis of the non-covalent interactions. The structural comparison showed that the different anions induce conformational changes of the macrocyclic structure, but only NO 3 − gave a true inclusion complex. Additionally, the tetramethylammonium derivative of 1 , [ 1-Me 4 ]I 2 ( 7 ), was prepared and structurally characterized. 1 H NMR titration studies of [ 1-H 2 ] 2+ in an aqueous–polar solvent mixture (H 2 O/MeOH, 9:1 v/v, pH 5.5) with a series of organic and inorganic anions gave association constants varying from 1.4 to 84.6 M −1 .
Sterol metabolism. XLI. Cholesterol A-ring autoxidations
Abstract Chromatographic and spectral evidence is adduced for the presence of cholest-5-en-3-one, cholest-4-en-3-one, and cholest-4-ene-3,6-dione in samples of cholesterol aged naturally in air or subjected to irradiation in air by 60 Co gamma radiation. These findings establish an additional mode of air oxidation of cholesterol to A-ring 3-ketones. Moreover, the oxidation by air of cholest-5-en-3-one induced by 60 Co gamma radiation yielded cholest-4-en-3-one, cholest-4-ene-3,6-dione, and the epimeric 3-oxocholest-4-ene-6-hydroperoxides. Cholest-4-en-3-one was not altered by irradiation in air, nor was cholesterol isomerized to cholest-4-en-3β-ol upon irradiation. From these observations it is deduced that the radiation-induced A-ring dehydrogenation of cholesterol yields initially cholest-5-en-3-one which upon isomerization yields cholest-4-en-3-one not further oxidized and which by a second oxidation yields the epimeric 3-oxocholest-4-ene-6-hydroperoxides which decompose to cholest-4-ene-3,6-dione.