[¹¹C]Carbon Monoxide in Selenium-Mediated Synthesis of ¹¹C-Carbamoyl Compounds

Abstract

Using either amines, amino alcohols, or alcohols in selenium-mediated synthesis with [(11)C]carbon monoxide, 3 ureas, 6 carbamates, and 1 carbonate were labeled. Tetrabutylammonium fluoride ((TBA)F) was discovered to form a soluble and reactive complex with selenium and drastically increase the radiochemical yields. Of the selected carbamoyl compounds, one was a receptor ligand, one was an enzyme inhibitor, and one was a muscular relaxant pharmaceutical. The (11)C-target compounds were obtained in radiochemical yields ranging from low to almost quantitative and with specific radioactivity up to 1300 GBq/micromol. The radiochemical purity of the final products exceeded 98%. In one case, the corresponding (13)C-substituted compound was produced to verify the position of the (11)C-label. In a typical experiment starting with 16.4 GBq [(11)C]carbon monoxide, 7.0 GBq of LC-purified 5-phenyl-1,3-oxazolidin-[2-(11)C]-2-one was obtained within 20 min from start of the carbonylation reaction (84% decay-corrected radiochemical yield). The presented approach is an interesting alternative to the use of [(11)C]phosgene in labeling chemistry.

Synthesis and Application of Isocyanates Radiolabeled with Carbon‐11

“…[ 11 C]CO 2 , produced by the 14 NA C H T U N G T R E N N U N G (p,a) 11 C nuclear reaction, was concentrated from the gas target in a stainless steel coil cooled to À178 8C. Upon warming, the [ 11 C]CO 2 in a stream of N 2 gas was passed through a NO x trapping column and a drying column of P 2 O 5 prior to use.…”

“…[9][10][11][12] In particular Brown et al [13] devised a clever way to overcome the formation of symmetrical [ 11 C]ureas, a common but undesirable side-reaction, by utilizing N-sulfinylamines as precursors. While reactive enough to add to phosgene, N-sulfinylamines are poor nucleophiles, thus suppressing further addition of amine to the generated [ [14] . [17] No additional examples were given and the method may be limited to aromatic amines and constrained by the lack of structurally diverse triphenylphosphinimines.…”

Selenium‐Catalyzed Reductive Carbonylation of 2‐Nitrophenols to2‐Benzoxazolones

“…Selenium has a very low solubility in most common solvents, but as the reaction proceeds it dissolves completely and the system become a brown homogeneous solution. [32,33] When the reaction is quenched by stopping bubbling CO and exposing the solution to air, the solution is oxidized to form a grey precipitate of selenium, which can be easily recovered by filtration and can be reused with a yield of 75 % to give a catalytic activity similar to that of fresh selenium. That is, the reaction system changes from heterogeneous to homogeneous and then recycles to heterogeneous to allow separation.…”

Synthesis of 11C‐/13C‐Ketones by Suzuki Coupling

“…So far, the most frequently used methods for introducing a 11 C unit into organic compounds are S-, O-and N-methylations using [ 11 C]methyl iodide or [ 11 C]methyl triflate, [1] while 11 CϪC bond forming reactions, such as the Grignard reaction using [ 11 C]carbon dioxide, [2] are less useful. Recently, however, 11 CϪC bond forming reactions using [ 11 C]carbon monoxide have become an increasingly employed 11 C-labelling strategy and a wide range of 11 C-labelled carbonyl compounds, such as ketones, [3] amides, [4] imides, [5] hydrazides, [6] carbamates, [7] and carboxylic acids [8] , have been synthesised using this method. [9] Transition metal-catalysed carbonylations using electrophiles, carbon monoxide and organostannanes [10] (Stille coupling) or organoboron compounds [11] (Suzuki coupling [12] ) are approaches that are used frequently for the synthesis of ketones.…”