13C-Labelled (±±)-Catechin From Potassium [13C]Cyanide

Gram-Scale Production and Applications of Optically Pure13C-Labelled (+)-Catechin and (−)-Epicatechin

“…Therefore, we significantly improved the yields in comparison with the other strategy (C 3 ϩ C 3 ϪC 6 ) [1] and furthermore, this route is asymmetric. Indeed, an efficient resolution of racemic benzylated catechin was used as the key step, allowing us to obtain the two antipodal series in high optical purity.…”

“…We recently applied this to the synthesis of racemic 4-[ 13 C]catechin (40 mg). [1] The more efficient and convenient second strategy was applicable on a larger scale, consisting in the crotonization reaction between a C 6 ϪC 2 acetophenone and a C 1 ϪC 6 benzaldehyde to form a chalcone. This formally allowed us to synthesize 13 C-labelled (Ϫ)-procyanidin B3, a dimer of catechin (30 mg).…”

“…[11] No purification was carried out on 11 which was immediately oxidized by an osmium-catalyzed diastereoselective dihydroxylation, providing 31 g of racemic 4-[ 13 C]flavan-3,4-diol 12 from 74 g of 10 (41% yield after crystallization). Deoxygenation at C-4 was carried out with NaBH 3 CN, [1,12] giving 24.3 g of racemic 4-[ 13 C]catechin tetrabenzyl ether 13 (81% yield).…”

“…As we have already presented in previous papers, [1,2] it would be very useful to dispose of 13 C-labelled catechin and epicatechin (1 and 2, Scheme 1) to assess the question of their resorption and to increase the knowledge of their metabolism in humans. Introduction of 13 C labelling requires the total synthesis of the skeleton, as described in earlier syntheses (monomer [1] and dimer B3 [3] ).…”

“…Introduction of 13 C labelling requires the total synthesis of the skeleton, as described in earlier syntheses (monomer [1] and dimer B3 [3] ). In addition, the problems posed by the stereochemistry at C-2 and C-3 must be overcome, [4] as has been achieved, for example, by chemical resolution of unlabelled racemic catechin with an -tartrate derivative.…”