Highly Efficient Dynamic Kinetic Resolution of Azlactones by Urea‐Based Bifunctional Organocatalysts

F420H2-Dependent Degradation of Aflatoxin and other Furanocoumarins Is Widespread throughout the Actinomycetales

“…The dihydro-furanocoumarin product may react with Tris by two methods, which may account for the two observed product peaks. Firstly, it may be ring opened by any one of the three hydroxyl groups of Tris by alcoholytic ring opening [28]. Secondly, the carbon associated with the ester functional group may be attacked by the amine via nucleophilic substitution.…”

Non‐racemic atropisomeric (thio)ureas as neutral enantioselective anion receptors for amino‐acid derivatives: Origin of smaller Kass with thiourea than urea derivatives

“…This could be taken as an indication of an H-bond in the case of the thiourea. Takemoto and coworkers 22 mentioned the intramolecular H-bond in thiourea to explain a better solubility of the catalyst and Berkessel et al 25 stated that there is no intramolecular Hbond in the urea. The fact that a stronger intramolecular H-bond is developed in the thiourea (3b) might account for the cases in which the thiourea catalyst, contrary to expectation, is less efficient than the urea analogue.…”

“…In 2005, Takemoto and coworkers 22 and Berkessel et al 25 published independently the X-ray structure of the thiourea (3b) and of the urea (3a), respectively. Inspection of the CIF files reveals that both urea and thiourea are in the crystal in a (Z,Z) conformation already suitable for a double binding; an interesting point is that in the thiourea the distance between the hydrogen of the NÀ ÀH and the nitrogen of the tertiary amine is shorter than in the urea analogue (2.69 Å versus 2.89 Å ).…”

“…25,26 Non-racemic chiral (thio)-ureas are also involved as ''neutral enantioselective anion receptors'' in molecular recognition aiming at the enantioselective binding of carboxylates. 27,28 In these enantioselective processes, the presence of two hydrogen bond donating (HBD) sites on the chiral (thio)urea plays a decisive role.…”

Recyclable Ligands for the Non‐Enzymatic Dynamic Kinetic Resolution of Challenging α‐Amino Acids

“…[6,7] Among various approaches to enantiomerically pure TMa-AAs, [6][7][8] the dynamic kinetic resolution (DKR) of racemates is unarguably the most economic solution, especially on alarge scale.[9] However,the choice of methods available for such processes is overwhelmingly dominated by biocatalytic procedures, [10] whereas purely chemical methods [11] have been disproportionally underdeveloped and prohibitively expensive.[12] Therefore,t osurpass the exceptional efficiencyo f enzymatic approaches, [10] ap urely chemical method should feature an ingenious combination of simple and high-yielding reactions,o perationally convenient conditions, [13] as well as inexpensive starting materials and ar ecyclable source of chirality.A sp art of our long-term interests in the development of practical methods for the preparation of TM-a-AAs and TM-b-AAs [14, 15] and drawing inspiration from work by Chin and co-workers, [16] we have recently been focusing on the development of new types of chiral ligands that are suitable for direct and practically useful DKR reactions of unprotected TM-a-AAs.In particular,compounds 1 and 2,which were reported by Chin [16] and co-workers and ourselves, [17] are considered as the best-performing ligands for the direct DKR of unprotected TM-a-AAs (Figure 1). Forb oth types of ligands,D KR proceeds via the corresponding Schiff base intermediates followed by thermodynamic equilibration of the resulting diastereomers.However,ligands 1 and 2 also share the same shortcomings:1 )They completely fail in the DKR of amino acids with tertiary side chains,a nd 2) as they are based on axially chiral 1,1'-binaphthyl moieties,they are rather expensive to rival the economic efficiencyofenzymatic methods for the large-scale preparation of TM-a-AAs.C ontinuing our work on modular approaches to chiral ligands, [18] we identi- Figure 1.…”