| dc.description | Methods have been developed to perform selective substitution on pentaerythritol, dipentaerythritol, tripentaerythritol and related compounds. Reaction of the di-O-benzylidene acetals of dipentaerythritol with benzyl chloride and potassium hydroxide surprisingly gave good to excellent yields of the mono-O-benzyl ethers. An explanation for this observation was advanced. The di-O-benzyl derivatives of the di-O-benzylidene acetals of dipentaerythritol were formed by reaction of their dianions with benzyl bromide in DMF. A purified mixture of the three possible benzylidene acetals of dipentaerythritol was successfully reduced to the corresponding di-O-benzyl ether with Et 3SiH/BF3.Et2O. Tripentaerythritol was converted efficiently and selectively into tri-O-benzylidene and tri- O-cyclohexylidene acetals. All of the four possible diastereomeric benzylidene acetals were formed and readily separated by column chromatography. Structures were assigned based on symmetry and on NMR parameters previously obtained for the three di-O-benzylidene acetals of dipentaerythritol. A purified mixture of the four possible benzylidene acetals of tripentaerythritol was also reduced to the corresponding tri-O-benzyl ether with Et3SiH/EtAlCl2. A method was developed for the synthesis of benzylated derivatives of polyols that contained one free hydroxyl group using stannylene acetal intermediates. This method gave the tri- O-benzyl ether from pentaerythritol efficiently. 2-Hydroxymethyl-2-methyl-1,3-propanediol gave the di-O-benzyl derivative in good yield. It was found that the remaining hydroxymethyl group of pentaerythritol tri-O-benzyl ether can be converted efficiently into an iodide atom, which in turn can be efficiently displaced by cyanide and azide ions. Michael reactions were performed with pentaerythritol tri-O-benzyl and tri- O-allyl ethers and acrylonitrile. Two improved routes have been developed to pentaerythritol mono-O-benzyl ether, reductive cleavage of the benzylidene ring of the mono-O-benzylidenepentaerythritol (12) using EtAlCl2 and Et3SiH and selective mono-O-benzylation of (12) followed by acidic hydrolysis. Pentaerythritol tri-O-allyl ether was efficiently converted to two potential glycosyl acceptors equipped with linker arms that allow further manipulation. Methods have been also developed to convert pentaerythritol into several unique types of mono-, di-, and trisubstituted derivatives. Some of these derivatives have been utilized to create a trivalent mannoside dendritic wedges. An approach to a novel glycodendrimer bearing nine mannose residues has been developed. The synthesis relies on the development of conditions which allowed the crucial triple Sonogashira coupling reaction of the dendritic wedge (75) and the tri-O-propargyl ether ( 80), prepared efficiently by two different methods, to proceed efficiently. The synthesis of the glycodendrimer was completed and the product was deprotected and fully characterized by NMR and FT-ICR mass spectrometry. | en_US |
