- Control of phosphoryl migratory transesterifications allows regioselecive access to sugar phosphates
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Phosphate esters in polyhydroxylated systems are normally blighted by uncontrolled migration under a variety of reaction conditions. Cesium fluoride is demonstrated as a reagent to control migration of primary phosphates during transesterifications. This allows easy exchange of phosphoryl protecting groups enabling enhanced synthetic strategic flexibility and regioselective phosphate installation. Mechanistic analysis suggests that a fluoride-induced extended solvent sphere modulates steric bulk at phosphorus to favor the primary position.
- Patel, Mitul K.,Davis, Benjamin G.
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supporting information
p. 346 - 349
(2013/03/14)
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- DIFFERENT ROTAMETER POPULATIONS AROUND THE C-5-C-6 BOND FOR α-AND β-D-GALACTOPYRANOSIDES THROUGH THE COMBINED INTERACTION OF THE GAUCH AND ANOMERIC EFFECTS: A 300-MHz 1H-N.M.R. AND MNDO STUDY
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A 300-MHz 1H-n.m.r. study of methyl 2,3,4-tri-O-methyl-α-(1) and -β-D-galactopyranoside 6-(dimethyl phosphate) (3), using various solvents, shows that the gauche (gg) rotamer populations about the C-5-C-6 bond are the same in all solvents, whereas those of the gauche(trans) (gt) and trans(gauche) (tg, O-5 and O-6 trans) rotamers are solvent dependent.The tg population increases with decreasing polarity of the solvent, which is attributed to an increased electrostatic repulsion between O-5 and O-6 in apolar-solvents.The tg population of 3 is larger than that of 1 and the same difference is observed in the corresponding compounds (2 and4) which have a trigonal-bipyramidal five coordinated phosphorous /P5) at position 6 and which have a higher electron density at O-6.These differences in rotamer populations are due to an effect additional to that of the coulombic effect between O-5 and O-6.That these differences are caused by a combination of the gauche and anomeric effects is supported by the finding that the tg population increases with increasing pKa of the group at C-1.The results of the n.m.r. measurements (in CCl4) are reproduced fairly accurated by MNDO calculations on model systems.The solvent dependence of the rotamer population around the C-5-C-6 bond is a good criterion for the assignment of the H-6S,6R resonances since, for galactopyranosides, J5,6S increases and J5,6R decreases as the polarity of the solvent decreases.
- Vries de, Nanne K.,Buck, Henk M.
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