Solvent interactions with β-Cyclodextrin as observed in crystal structures

Nimesulide, an anti-inflammatory drug, was complexed with β cyclodextrin (βCD) in the presence of lysine in 10:10:1 molar ratio to increase its water solubility. The complexation did not take place in the crystal structure, but it exhibits two different crystal forms. The crystal structures show a difference in hydration pattern and conservation of the organic molecule 2,4 methyl pentane diol (MPD) binding site. Molecular mechanics studies carried out suggest a probable mode of binding of nimesulide with βCD

Ethyl 2-formamido-2-(4-iodobenzyl)-3-(4-iodophenyl)propionate and ethyl 2-(3-bromobenzyl)-3-(3-bromophenyl)-2-formamidopropionate

The title compounds, C19H19I2NO3 and C19H19Br2NO3, are derivatives of alpha-aminoisobutyric acid with halogen substituents at the para and meta positions, respectively. The ethoxycarbonyl and formamide side chains attached to the C-alpha atom of the molecule adopt extended and folded conformations, respectively. The crystal structures are stabilized by N-H...O, C-H...O, C-Br...O and C-I...O interactions

Conformational switching caused by biphenyl substitution at the C-a position: ethyl 2-benzyl-2-(formylamino)-3-phenylpropionate and ethyl 3-(1,1 '-biphenyl-4-yl)-2-(formylamino)-2-(4-phenylbenzyl)propionate

The title compounds, C19H21NO3 and C31H29NO3, are derivatives of alpha-aminoisobutyric acid, with benzyl and dibenzyl substitution. The pseudo-peptide formed by the N-formyl and ethyl ester substitution at the C-alpha position switches from a trans - trans to a trans - cis configuration as a result of biphenyl substitution. The packing of the compounds is stabilized by N - H...O and C - H...O hydrogen bonds

Precursors to dodecahedrane

The title compounds, (2R,2"S,3b'S,4a'R,7b'S,8a'R)-perhydrodispiro[furan-2,3'-dicyclopenta[a,e]pentalene-7',2"-furan]- 5,5"-dione, C20H26O4, and (3aR,3bR,4aR,4bS,5aS,8aR,8bR, 9aR,9bS,10aS)-perhydrodipentaleno [2,1-a:2',1'-e] pentalene-1,6-dione, C20H26O2, are intermediates identified during the synthesis of dodecahedrane. Crystallographic studies have established the ring-junction stereochemistry for these important intermediates. All the ring junctions are cis-fused, and the molecular packing is stabilized by van der Waals interactions

Conformational effects of C-alpha,C-alpha-dipropargylglycine as a constrained residue

A useful synthon to approach artificial phenylalanyl peptides in a [2 + 2 + 2] cycloaddition reaction, C-alpha,C-alpha-dipropargylglycine (Dprg) is examined for its conformational preferences as a constrained residue. Crystal structure analysis and preliminary NMR results establish possible preference of the residue for folded (alpha) rather than extended (beta) region of the phi,psi conformational space. Boc-Dprg-L-Leu-OMe (1) displays two molecular conformations within the same crystallographic asymmetric unit, with Dprg in the alpha (R) or alpha (L) conformation, participating in a type I beta -turn or an alpha (L)-alpha (R)-type fold, in which Leu(2) assumes the alpha (R) conformation stereochemically favored for an L-chiral residue. Boc-Dprg-D-Val-L-Leu-OMe (2) displays a type I ' beta -turn conformation in crystal, with both Dprg(1) and D-Val(2) assuming the alpha (L) conformation stereochemically favored for a D-chiral residue, with 4 --> 1 type hydrogen bond linking L-Leu(3) NH is with Boc CO. NMR analysis using temperature variation, solvent titration, and a spin probe study suggests a fully soh,ent-exposed nature of Dprg NH, ruling out a fully extended C-5-type conformation for this residue, and soli,ent sequestered nature of L-Leu(3) NH, suggesting possibility of a beta -turn due to Dprg assuming a folded conformation. (C) 2001 , Inc

Ethyl 6-acetylamino-6,7-dihydro-5H-dibenzo[a,c]cycloheptene-6-carboxylate

The title compound, C20H21NO3, is a derivative of Aib (alpha-aminoisobutyric acid) and is cyclized at the C-alpha position by biphenyl rings. The seven-membered ring possesses C2 symmetry. The C-alpha cyclization causes the backbone to assume a helical conformation in the crystal structure. The packing of the molecules is stabilized by intermolecular C-H...O, C-H...pi and N-H...O hydrogen bonds

anti-2,19-diethoxycarbonyl-2,19-diformyl-amino[3.2.3.2]paracyclophane

The title compound, C42H46N2O6, crystallizes with half a molecule in the asymmetric unit, the molecule being centrosymmetric. The ethyl ester and N-formyl side chains attached to the C-alpha atom of the molecule adopt a trans and cis configuration, respectively. The crystal structure is stabilized by C-H...O, N-H...O and C-H...pi interactions and herring-bone-type packing is observed

Conformational preferences of heterochiral peptides. Crystal structures of heterochiral peptides Boc-(D) Val-(D) Ala-Leu-Ala-OMe and Boc-Val-Ala-Leu-(D) Ala-OMe- enhanced stability of beta-sheet through C-H - O hydrogen bonds

The crystal structures of Boc-(D) Val-(D) Ala-Leu-Ala-OMe (vaLA) and Boc-Val-Ala-Leu-(D) Ala-OMe (VALa) have been derermined. vaLA crystallises in space group P2(1)2(1)2(1) with a = 9.401 (4), b = 17.253 (5). c = 36.276 (9)Angstrom, V = 5884 (3) Angstrom (3), Z = 8, R = 0.086. VALa crystallises in space group p2(1)2(1)2(1) with a = 9.683 (9), b = 17.355 (7), c = 18.187 (9) Angstrom, beta = 95.84 (8)degrees, V = 3040(4) Angstrom (3), Z = 4. R = 0.125. There are two molecules in the asymmetric unit in antiparallel P-sheet arrangement in both the structures. Several of the Ca hydrogens are in hydrogen bonding contact with the carbonyl oxygen in the adjacent strand. An analysis of the observed conformational feature of D-chiral amino acid residues in oligopeptides. using coordinates of 123 crystal structures selected from the 1998 release of CSD has been carried out. This shows that all the residues except D-isoleucine prefer both extended and a, conformation though the frequence of occurence may not be equal. In addition to this, D-leucine, valine, proline and phenylalanine have assumed cc, conformations in solid slate. D-leucine has a strong preference for helical conformation in linear peptides whereas they prefer an extended conformation in cyclic peptides