SidA from the human pathogen Aspergillus fumigatus catalyzes the generation of N(5)-hydroxyornithine in the biosynthesis of siderophores, a reaction essential for virulence. The crystal structures of SidA in complex with ornithine and lysine reveal the geometry of the interactions among flavin, NADP(+), and the substrate amine group that underlie the hydroxylation reaction. The structural elucidation of the enzyme in complex with arginine provides insight into the role of electrostatics and hydrogen bonding in the mechanism of oxygen activation in this family of enzymes.
Octaphenylnaphthalene (2) was synthesized by the addition of tetraphenylbenzyne to tetraphenylcyclopentadienone, and decaphenylanthracene (3) was synthesized by the addition of the same aryne to hexaphenylisobenzofuran followed by deoxygenation of the adduct. The structures of both compounds were determined by X-ray analysis. Compound 2 adopts a conformation of approximate C i symmetry with a slightly undulating naphthalene nucleus, but compound 3 exhibits C 2 (and approximate D 2 ) symmetry with a 63°twist of the central anthracene.
9,10,11,20,21,22-Hexaphenyltetrabenzo[a,c,l,n]pentacene (1) was prepared by the reaction of 1,3-diphenylphenanthro[9,10-c]furan with the bisaryne equivalent generated from 1,2,4,5-tetrabromo-3,6-diphenylbenzene in the presence of n-butyllithium, followed by deoxygenation of the double adduct with low-valent titanium. The X-ray structure of 1 shows it to be the most highly twisted polycyclic aromatic hydrocarbon known, with an end-to-end twist of 143.6 degrees . Compound 1 was resolved by chromatography on a chiral support, and the pure enantiomers have specific rotations in excess of 7000 degrees , but the molecule racemizes slowly at 25 degrees C (t1/2 = 9.3 h, DeltaGrac = 23.8 kcal/mol).
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