A Convenient Synthesis of Conformationally Constrained β-Substituted Tryptophans

Direct chiral separation of unnatural amino acids by high‐performance liquid chromatography on a ristocetin a‐bonded stationary phase

“…34,35 The synthesis of 2Ј-methylphenylalanine (7; 2-MePhe), 36 4Ј-methylphenylalanine (8; 4-MePhe), 3 7 2Ј,6Јdimethylphenylalanine (9; 2,6-diMePhe), 36 The following analytes were synthesized as racemates: erythro-(2S,3S and 2R,3R)-␤-methylphenylalanine (11; erythro-␤-MePhe), 3 9 threo-(2S,3R and 2R,3S)-␤methylphenylalanine (12; threo-␤-MePhe), 39 2Ј,6Јdimethyltyrosine (2; 2 ,6 -diMeTyr), 4 0 2 Ј ,6Јdimethyltyrosineamide (3; 2,6-diMeTyrNH 2 ), 41 erythro-(2S,3S and 2R,3R)-␤-methyltyrosine (5; erythro-␤-MeTyr), 42 threo-(2S,3R and 2R,3S)-␤-methyltyrosine (6; threo-␤-MeTyr), 42 1,2,3,4-tetrahydroisoquinoline-1carboxylic acid (13; Tic1), 4 3 6Јhydroxy-1,2,3,4tetrahydroisoquinoline-3-carboxylic acid (15; 6-HO-Tic3), 38 erythro-(2S,3S and 2R,3R)-4-methyl-1,2,3,4tetrahydroisoquinoline-3-carboxylic acid (19; erythro-␤-MeTic3), 38 threo-(2S,3R and 2R,3S)-4-methyl-1,2,3,4tetrahydroisoquinoline-3-carboxylic acid (20; threo-␤-MeTic3), 38 2-aminotetralin-2-carboxylic acid (21; Atc), 44 6-hydroxy-2-aminotetralin-2-carboxylic acid (22; Hat), 45 6-methoxy-2-aminotetralin-2-carboxylic acid (23; MeO-Atc), 45 erythro-(2S,3S and 2R,3R)-␤-methyltryptophan (24; erythro-␤-MeTrp), 4 6 threo-(2S,3R and 2R,3S)-␤methyltryptophan (25; threo-␤-MeTrp). 46 The physicochemical data of amino acids synthesized were determined and were identical with the data cited in references 36-46, respectively, except for analyte 3. Its melting point was 164.9-167.7°C, R f value in TLC was 0.57 in butanol/ acetonitrile/water = 4/1/1 (v/v/v) and by electrospray ionization mass spectrometry in the positive mode the molecular ion [M + H] + was detected at 209.13 Da/e.…”

para‐Toluenesulfonic Acid‐Catalyzed, Ultrasound‐Promoted, One‐Pot, Three‐Component Coupling of Aldehydes, β‐Dicarbonyls/Amides, and Electron‐Rich Arenes

“…In 1978, Yonemitsu developed a one‐pot three component coupling of aldehydes, Meldrum's acid, and indoles to generate biologically relevant motifs . Since then, several methods of Yonemitsu reactions are reported using Brønsted bases such as d,l ‐proline or Lewis acidic species such as TiCl 4 , Yb(OTf) 3 or Eu(OTf) 3 . Recently, heterogeneous catalysts such as hydromagnesite rectangular thin sheets, Fe 3 O 4 @SiO 2 ‐PEG/NH 2 , and graphene oxide supported ionic liquids, have been developed for this particular three‐component coupling reaction.…”

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

“…10 Since the pioneering work of Snyder, 11 a large number of attempts at the synthesis of b-MeTrp have been undertaken. 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.…”