Deprotonation of large calixarenes-cation binding and conformations

© 2016 CSIRO. Single crystal X-ray studies of p-t-butylcalix[10]arene·2dmso·7H2O (1) and [NMe4][p-t-butylcalix[9]arene-H]·2dmso·H2O (2), provide new data on these large macrocycles and their conformations, that of 2 being the first where an encapsulated [NMe4]+ cation is present, while 1 contains the neutral ligand. Both were obtained as crystalline products of the reactions of the calixarenes with tetramethylammonium hydroxide after prolonged standing. The structure of [NEt4][calix[4]arene-H], in which the cation approaches inclusion in the shallow cone of the anion, is also defined and compared with various other alkylammonium derivatives of calixarenes as well as that of p-t-butylcalix[9]arene

A comparison of the conformations adopted by some 5-bromovinyl-2'-deoxyuridines and a correlation with their antiviral properties: an X-ray study.

Crystal structures of (Z)-5-(2-bromovinyl)-2'-deoxyuridine, 3',5'-di-O-acetyl-(E)-5-(2-bromovinyl)-2'-deoxyuridine and 3',5'-di-O-p-chlorobenzoyl-5-(2-dibromovinyl)-2'-deoxyuridine are compared with each other and with that of the most potent antiviral agent (E)-5-(2-bromovinyl)-2'-deoxyuridine (E-BVDU) reported earlier. A comparison of the conformation of 3',5'-di-O-acetyl-pyrimidine nucleoside structures in which intermolecular hydrogen bond network formation is minimized, with those of their parent compounds has shown that the greatest change in rotation about the glycosyl bond and in the sugar ring pucker is exhibited by E-BVDU. Upon acylation this molecule changes from C2'-endo/C3'-exo conformation to C3'-endo/C4'-exo conformation. The relevance of these structures upon the biological activity of the nucleosides and in particular to their ability to be a substrate for thymidine kinase is discussed

Extremely short H···H distances and intermolecular hydrogen-bonding patterns of dialkyl α-aryl-α-(diphenylmethylamino)methanephosphonates

<p>Single crystal X-ray diffraction studies of four <i>N</i>-benzhydryl protected diethyl α-amino-α-arylmethanephosphonates (aryl = phenyl, 1-naphthyl, 1-anthryl, and 1-pyrenyl) reveal several distinct types of hydrogen bonding, leading to the formation of (a) dimers containing two molecules of the same stereochemistry (<i>SS</i> or <i>RR</i>) in one case, (b) centrosymmetric dimers containing two enantiomeric molecules (<i>RS</i>) (both involving P=O···H–N interactions) in two crystals, and (c) in the anthryl derivative, a short intramolecular C–H···O=P contact distance but no involvement of the amino N–H. The anthryl derivative forms chains of molecules, with a possible interaction between phosphoryl oxygen and a phenyl hydrogen atom of one of the benzhydryl groups in an adjacent molecule. These molecules adopt a staggered conformation about the C–P bond, with the H atom of the chiral α-carbon atom approximately anti to the N–H. A further peculiarity is in the extremely short approaches of the “shoulder” H-atoms of the 1-naphthyl, 1-anthryl, and 1-pyrenyl moieties to the chiral α-carbon H atom at about 0.4–0.6 Å shorter than the sum of the van der Waals radii. In the 1-anthryl substituted crystal, a similar short approach to the N–H might be a reason for the vanishing N–H···O=P hydrogen bond.</p