- A selective process for n-alkylation in competition with o-alkylation: Boric acid, borax, and metaborate as a cheap and effective protecting group applicable for industrial-scale synthetic processes
-
This paper describes a selective process for the N-alkylation of substrates that contain 1,2-diol groups. The developed approach utilises temporary protection of the diol groups by boric acid, Borax, or metaborate. The introduction of the boron-containing groups into the substrate may provide, in addition to affording the intended protection of the hydroxyl groups that may otherwise act as nucleophilic sites, the advantages of improved solubility of the substrate in water that is used as solvent. Moreover the N-alkylation and the deprotection of the diols are performed in one pot, and the formation of undesired O-alkylated by-products is significantly reduced. The paper gives examples from the synthesis of several X-ray contrast agents used in medical imaging diagnostics: iohexol (Ominipaque, Nycomed Imaging); iopentol (Imagopaque, Nycomed Imaging); iodixanol (Visipaque, Nycomed Imaging); ioversol (Optiray, Mallinckrodt).
- Bjorsvik, Hans-Rene,Priebe, Hanno,Cervenka, Jan,Aabye, Arne W.,Gulbrandsen, Trygve,Bryde, Arnt Christian
-
p. 472 - 478
(2013/09/07)
-
- An Observation of Cationic Influence on the N/O Alkylation Selectivity in the Alkylation of a Compound Containing Several Nucleophilic Sites
-
The reaction of N,N'-bis(2,3-dihydroxypropyl)-5-acetamido-2,4,6-triiodoisophthalamide 1 with 3-chloro-1-methoxy-2-propanol 2 has been studied.In addition to the desired product N,N'-bis(2,3-dihydroxypropyl)-5--2,4,6-triiodoisophthalamide 3, which is a pharmaceutical agent of interest as a general purpose X-ray contrast agent in medical imaging, several by-products were also formed.The by-products were formed by concomitant alkylation of other nucleophilic sites.The yield of 3 and the by-products was found to be influenced by the presence of various cations during the alkylation step.It was found that Ca++ showed the most promising results, giving the highest yield of 3 as well as affording the best selectivity.The response surface technique was used to analyze which variables influenced the desired reaction and the competing reactions.Response surface models were used to predict a detailed setting of the variables for an optimal synthetic procedure.
- Bjoersvik, Hans-Rene,Aabye, Arne Wang,Carlson, Rolf,Carlsen, Per
-
p. 582 - 588
(2007/10/02)
-