Biomedical subjects
Publications and source records attributed to Steven Dell.
Currently, two single optic accommodative intraocular lenses are available for implantation. Both designs rely on the interaction of the ciliary muscle with the zonule and capsule to induce axial movement of the optic. This article reviews the historical development, laboratory data, and clinical findings relating to these interesting devices.
DABCO is an extremely active catalyst for the methylation of indoles in conjunction with dimethyl carbonate (DMC). This green chemistry is highly effective and produces N-methylindoles in nearly quantitative yields. The reaction sequence consists of competing alkylation and acylation pathways and involves 1,4-diazabicyclo[2.2.2]octane (DABCO) dually as a nucleophilic catalyst, ultimately resulting in a single product: the N-methylated indole.
1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) is an effective nucleophilic catalyst for carboxylic acid esterification with dimethyl carbonate (DMC). The reaction pathway of this new class of nucleophilic catalysis has been studied. A plausible, multistep mechanism is proposed, which involves an initial N-acylation of DBU with DMC to form a carbamate intermediate. Subsequent O-alkylation of the carboxylate with this intermediate generates the corresponding methyl ester in excellent yield. In the absence of DBU or in the presence of other bases, such as ammonium hydroxide or N-methylmorpholine, the same reaction affords no desired product. This method is particularly valuable for the synthesis of methyl esters that contain acid-sensitive functionality.
The syntheses of several cyclophanes containing a triaryl(element) "top" poised above a trisubstituted benzene "base" were carried out to install a non-hydrogen atom as a substituent on a bridgehead with an inwardly directed geometry. Most significantly, the tribenzo 6-fluoro-6-sila-2,10,19-trithia[5(6,14)][11]metacyclophane 2 was prepared by condensation of tris[2-(bromomethyl)phenyl]fluorosilane and 1,3,5-tris(mercaptomethyl)benzene in 0.4% yield. The X-ray structure of 2 shows that the cyclophane adopts an in-configuration; i.e., the fluorine atom is on the interior of the macrocycle and only 2.8 Å from the center of the basal aromatic ring. Compound 2 is one of only a very few molecules to contain a non-hydrogen in-atom, and the in-fluorosilane of 2 is the largest in-functional group to have been installed in any molecule. Similar attempts to prepare an in-phosphine oxide were unsuccessful, although the corresponding in-phosphines were prepared, and an attempt to prepare an in-methylsilane led instead to the corresponding out-isomer.