“…In the reaction of 66 with acetone silyl enolate, both chemical yield and selectivity slightly decreased. The products in these reactions (alanine derivatives) are known as potent inhibitors of kynurenine 3-hydroxylase and kynureninase and expected to be potential drugs for the treatment of neurodegenerative disorders that function by controlling the concentration of quinolonic acid in the brain. , 2 …”
“…The products in these reactions (alanine derivatives) are known as potent inhibitors of kynurenine 3-hydroxylase and kynureninase and expected to be potential drugs for the treatment of neurodegenerative disorders that function by controlling the concentration of quinolonic acid in the brain. 87,88 It was shown that water played an important role in Sodeoka's system. Namely, water activated the Pd(II) complex to generate a cation complex, and also cleaved N-Pd bond of 68 to regenerate the chiral catalyst.…”
“…In the reaction of 66 with acetone silyl enolate, both chemical yield and selectivity slightly decreased. The products in these reactions (alanine derivatives) are known as potent inhibitors of kynurenine 3-hydroxylase and kynureninase and expected to be potential drugs for the treatment of neurodegenerative disorders that function by controlling the concentration of quinolonic acid in the brain. , 2 …”
“…The products in these reactions (alanine derivatives) are known as potent inhibitors of kynurenine 3-hydroxylase and kynureninase and expected to be potential drugs for the treatment of neurodegenerative disorders that function by controlling the concentration of quinolonic acid in the brain. 87,88 It was shown that water played an important role in Sodeoka's system. Namely, water activated the Pd(II) complex to generate a cation complex, and also cleaved N-Pd bond of 68 to regenerate the chiral catalyst.…”
“…The optically active 5 made available by this novel reaction has various potential applications. Substituted or unsubstituted benzoylalanines obtained by simple deprotection of 5 are known to be potent inhibitors of kynurenine 3-hydroxylase and kynureninase, potential drugs for the treatment of neurodegenerative disorders that function by controlling the toxic quinolinic acid concentration in the brain . Since the carbonyl group in 5 would allow various modificationssuch as reduction, alkylation, alkenylation, ketal formation, halogenation, etc.the acylalanine derivatives 5 are also expected to be important synthetic intermediates for a wide variety of nonnatural amino acids.…”
Studies on the enantioselective addition of enol silyl ethers to imines catalyzed by optically active
palladium diaquo complexes 3 or binuclear palladium μ-hydroxo complex 4 are described, with particular
focus on the mechanistic aspects. Asymmetric induction in the reaction using [Pd((R)-binap)(H2O)2]2+(BF4
-)2
(3a) was quite sensitive to the reaction conditions, suggesting unfavorable effects of HBF4 generated from 3a
in situ. Novel optically active binuclear μ-hydroxo complexes [{Pd((R)-binap)(μ-OH)}2]2+(BF4
-)2 (4a), [{Pd((R)-tol-binap)(μ-OH)}2]2+(BF4
-)2 (4b), [{Pd((R)-binap)(μ-OH)}2]2+(TfO-)2 (4c), and [{Pd((R)-tol-binap)(μ-OH)}2]2+(TfO-)2 (4d) were prepared and were found to be better catalysts for the asymmetric Mannich-type
reaction. Benzoylalanine derivatives 5 were obtained in excellent chemical and optical yields (up to 90% ee).
Mechanistic studies using 1H NMR and electrospray ionization mass spectrometry indicated that a unique
binuclear palladium-sandwiched enolate 12 was involved in the reaction of enol silyl ether 1 with imine 2
catalyzed by 4.
“…Deprotection of the N-Boc Mannich-type adduct 6b was easily performed under standard conditions to give the hydrochloride salt of the free amine 8 quantitatively without racemization (eq 2). 12 Mannich-type adducts 7e and 7f were also successfully transformed to m-NBA 13 (9e) and FCE28833 14 (9f), respectively, in excellent yields (eq 3). A single recrystallization of 9e and 9f increased the enantio-meric purity to 98 and 95% ee, respectively.…”
[reaction: see text] Catalytic, enantioselective Mannich-type reactions of alpha-imino esters bearing readily removable substituents on nitrogen are described. Several N-carbamate-protected alpha-imino esters, which are readily prepared from 2-bromoglycine esters using a polymer-supported amine, reacted with silicon enolates to afford the desired adducts in high yields with high enantioselectivity using a copper(II)-diamine complex. Easy deprotection of the product amine and transformation to free alpha-amino acid derivatives have also been demonstrated.
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