A Versatile Asymmetric Synthesis of .beta.-Branched .alpha.-Amino Acids

Diastereoselective Synthesis of 2-Amino-4-phosphonobutanoic Acids by Conjugate Addition of Lithiated Schöllkopf's Bislactim Ethers to Vinylphosphonates

“…15 -Substituted 1-vinylphosphonates with (Z)-configuration, 7da,fa-ja, were stereospecifically synthesized by either the acidic cleavage of (E)-R-triphenylstannylvinylphosphonates 7fq-hq 16 or the Pd(0)-catalyzed coupling of diethyl phosphite and (Z)-1-bromo-1-alkenes 17 13d,i,j (see Scheme 3). The required R-stannylvinylphosphonates were obtained by condensation of isovaleraldehyde (10f), isobutyraldehyde (10g), and benzaldehyde (10h) with R-bis(triphenylstan-(10) (a) Shapiro, G.;Buechler, D.;Ojea, V.;Pombo-Villar, E.;Ruiz, M.;Weber, H.-P. Tetrahedron Lett. 1993, 34, 6255-6258.…”

“…(b) Minowa, N.;Hirayama, M.;Fukatsu, S. Tetrahedron Lett. 1984, 25, 1147-1150 (11) Ojea, V.; Ruiz, M.; Shapiro, G.;Pombo-Villar, E. J. Org. Chem.…”

Stereochemical Study on α-Alkylation of β-Branched α-Amino Acid Derivatives­ via Memory of Chirality

“…Potassium hexamethyldisilazide (KHMDS) 17 (0.53 M in THF, 1.81 mL, 0.95 mmol) was added to a solution of (2R,3R)-N-tert-butoxycarbonyl-b-methylphenylalanine ethyl ester (307mg, 1.0 mmol) 18 in THF (5 mL) at -78°C. After 30 min, di-tert-butyl dicarbonate (436 mg, 2.0 mmol) was added and the mixture was gradually warmed to r.t. during a period of 20 h. The mixture was poured into aq NH 4 Cl (20 mL) and extracted with EtOAc (150 mL).…”

“…Prepared from (2S,3R)-N-tert-butoxycarbonyl-b-methylphenylalanine ethyl ester 18 according to the procedure for (2R,3R)-N,Nbis(tert-butoxycarbonyl)-b-methylphenylalanine ethyl ester in 77% yield.…”

A practical synthesis of enantiopure β-methyltryptophan ethyl ester for a preparation of diabetes drug

“…12,13 For example, optically active b-MeTrp has been prepared by classical resolution via diastereomeric salt formation 14,15 and by kinetic resolution using enzymatic hydrolysis. 16 Although enantioselective syntheses of bMeTrp were also reported, [17][18][19][20] from the viewpoint of large-scale production, these methods have significant drawbacks, such as the requirement of long synthetic steps, manipulation of expensive chiral auxiliaries, and usage of multiple protective groups.…”