Asymmetric synthesis using enantiomerically pure 2-(p-anisylsulfinyl)-2-cycloalkenones

Conjugate additions of many organometallic reagents to 2-(p-anisylsulfinyl)-2-cycloalkenones, 2 proceed with much greater diastereoselectivity than additions to the corresponding 2-(p-tolylsulfinyl)-2-cycloalkenones, 7. Complexation of 2 with zinc dibromide followed by addition of various Grignard reagents lead, after reductive removal of the sulfoxide, to 3-substituted cycloalkanones of higher optical purity than those obtained from 7. Addition of methyltitanium triisopropoxide to 2-(p-anisylsulfnyl)-2-cyclohexenone, 2b, in the absence of zinc dibromide, proceeds with virtually complete asymmetric induction.     

Enantioselective synthesis of 2-hydroxy-1-indanone,a key precursor of enantiomerically pure 1-amino-2-indanol

Enantiomerically pure (R)- or (S)-2-hydroxy-1-indanone was synthesized by enzymatic kinetic resolution of racemic 2-acetoxy-1-indanone through hydrolysis or transesterification.     

Synthesis of enantiomerically and diastereomerically pure 2(S)-amino-6(R)-hydroxy-1,7-heptanedioic acid dimethyl ester hydrochloride from cycloheptadiene

The complete carbon framework of enantiomerically and diastereomerically pure 2(S)-amino-6(R)-hydroxy-1,7-heptanedioic acid dimethyl ester hydrochloride was derived from cycloheptadiene in six steps utilizing an amino acid-derived acylnitroso Diels-Alder reaction as the key step. This versatile amino diester has been previously used to synthesize amino-differentiated diaminopimelic acid (DAP) and biologically active analogues. In addition, after formation of a novel aminoxy diketopiperazine, the newly formed carboxyl groups were differentiated by a novel transpeptidation of the amino acid that directed the stereochemistry of the initial cycloaddition.     

An efficient approach to the synthesis of enantiomerically pure trans-1-amino-2-(hydroxymethyl)cyclopropanephosphonic acids

The synthesis of (1R,2S)- and (1S,2R)-1-amino-2-(hydroxymethyl)cyclopropanephosphonic acids was accomplished using different strategies. The (1R,2S)-stereoisomer could be efficiently obtained by the cyclopropanation of ethyl diethoxyphosphorylacetate with the cyclic sulfate derived from (S)-3-benzyloxy-1,2-propandiol as a key step. The (1S,2R)-stereoisomer was synthesized from a readily available (1S,5R)-3-oxabicyclo[3.1.0]hexan-2-on-1-phosphonate.     

Asymmetric synthesis of 3-amino-4-hydroxy-2-(hydroxymethyl)pyrrolidines as potential glycosidase inhibitors

Three diastereoisomers of 3-amino-4-hydroxy-2-(hydroxymethyl)pyrrolidine have been synthesised by a divergent route starting from trans-4-hydroxy-L-proline. Regio- and stereoselective introduction of the 3-amino and 4-hydroxyl functional groups was achieved using either a tethered aminohydroxylation reaction or by employing intra- and intermolecular epoxide-opening strategies. Preliminary biological data indicate that two of these novel amino pyrrolidines are moderate inhibitors of beta-galactosidase.     

Synthesis of enantiomerically pure diethyl (R)- and (S)-2-hydroxy-3-(1,2,3-triazol-1-yl)propylphosphonates

The synthesis and ee determination of diethyl 3-azido-2-hydroxypropylphosphonates from 2,3-epoxypropylphosphonates have been optimised. Enantiomerically enriched diethyl (R)- and (S)-2-hydroxy-3-(1,2,3-triazol-1-yl)propylphosphonates (R)-3a–j and (S)-3a–h as well as (S)-3j were synthesised from diethyl (R)- and (S)-2,3-epoxypropylphosphonates in a reaction sequence including azidolysis followed by 1,3-dipolar cycloaddition with selected alkynes.     

Preparation of enantiomerically pure (R)- and (S)-3-amino-3-phenyl-1-propanol via resolution with immobilized penicillin G acylase

Ethyl 2,4-dioxo-4-phenylbutyrate, obtained by condensation of acetophenone with diethyl oxalate, was converted to 3-oxo-3-phenyl-1-propanol in 90% yield by reaction with baker’s yeast. Reductive amination with sodium cyanoborohydride in the presence of ammonium acetate gave the racemic 3-amino-3-phenyl-1-propanol in 65% yield. Enzymatic resolution of the corresponding N-phenylacetyl derivative with penicillin G acylase, immobilized on an epoxy resin gave (S)-amide and (R)-amino alcohol in high enantiomeric purity (ee >99%) and >45% yields for each enantiomer.     

Preparation of enantiomerically pure (1S,2S)-1-aminocyclopropanephosphonic acid from methylcyclopropanone acetal via spirophosphonate intermediates

An easy and efficient one-pot reaction from readily available methylcyclopropanone acetal (2S)-4b gave the spirophosphonates 8a–b with excellent diastereoselectivity. These phosphonates, after catalytic hydrogenolysis and hydrolysis, furnished the enantiomerically pure (1S,2S)-1-amino-2-methylcyclopropanephosphonic acid 3b (analogue of (1R,2S)-allo-norcoronamic acid).     

New synthesis of enantiomerically pure (S)-3-amino-2-phenyl propanoic acid via the asymmetric transformation of its racemic N-phthaloyl derivative

The synthesis of racemic N-phthalyl 3-amino-2-phenyl propanoic acid and its asymmetric transformation via the corresponding prochiral ketene have been investigated, allowing the preparation of enantiomerically pure (S)-3-amino-2-phenyl propanoic acid.     

Stereoselective synthesis of enantiomerically pure 1-(E)-alkenylsulfoximines

Optically active (E)-N-tosyl-S-(1-alkenyl)-S-phenylsulfoximines 4 are synthesized stereoselectively in a one pot sequence from readily available 1 via C-silylation, metallation and reaction of the corresponding lithiosulfoximine 3 with various carbonyl compounds. The El-MS spectra of the so prepared alkenylsulfoximines 4 show unexpected fragmentations, pointing to a new, unusual S-O-migration of the 1-alkenyl moiety.     

Synthesis of 1-(1-Adamantyl)-2-hydroxy-3-amino-3-R-propanones

Previously unknown cis-1-(1-adamantyl)-2,3-epoxy-3-R-propanones were highly selectively obtained by epoxidation of ,-unsaturated ketones with hydrogen peroxide in alkaline medium. The regioselectivity of the epoxide ring cleavage with amines (piperidine and morpholine) was studied.     

Biotransformation-mediated synthesis of (1S)-1-(2,6-dichloro-3-fluorophenyl)ethanol in enantiomerically pure form

An efficient four-step biotransformation-mediated synthesis of (1S)-1-(2,6-dichloro-3-fluorophenyl)ethanol in enantiomerically pure form is described. This compound is a key intermediate required for the preparation of PF-2341066, a potent inhibitor of c-Met/ALK that is currently in clinical development. The described synthesis was used to manufacture 6 kg of the title compound and can also be employed to produce the corresponding (1R)-enantiomer.     

Remote asymmetric trifluoromethylation induced by chiral sulfinyl group: synthesis of enantiomerically pure 1-(2-naphthyl)-2,2,2-trifluoroethanol

The reaction of 1-[(2,4,6-triisopropylphenyl)sulfinyl]-2-naphthaldehyde with (trifluoromethyl)trimethylsilane using tetramethylammonium fluoride gave trifluoromethylated compounds in high yield with high diastereoselectivity. Desilylation and subsequent recrystallization yielded the enantiomerically and diastereomerically pure trifluoroethanol, which afforded chiral 1-(2-naphthyl)-2,2,2-trifluoroethanol after removal of the sulfinyl group.     

An expedient synthesis of (±)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid hydrobromide via a 3-bromoisoxazole intermediate

The excitatory, amino acid ±2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid hydrobromide was prepared in gram quantities in an 3.3% overall yield from methylbut 2-ynoate. The key step was the facile preparation of methyl 3-bromo-5-methylisoxazole-4-carboxylate.     

A simple and practical approach to enantiomerically pure (S)-3-hydroxy-γ-butyrolactone: synthesis of (R)-4-cyano-3-hydroxybutyric acid ethyl ester

The oxidation of α- or β-(1,4) linked disaccharides or oligosaccharides with cumene hydroperoxide in the presence of a base gave (S)-3,4-dihydroxybutyric acid, which was cyclized under acidic conditions to furnish (S)-3-hydroxy-γ-butyrolactone. This was subsequently converted into (R)-cyano-3-hydroxybutyric acid ethyl ester, an intermediate for statin based drugs and other related compounds.     

Asymmetric synthesis and σ receptor affinity of enantiomerically pure 1,4-disubstituted tetrahydro-1H-3-benzazepines

A very short (three steps) asymmetric synthesis of enantiomerically pure 1,4-disubstituted tetrahydro-1H-3-benzazepines 14 has been elaborated upon, starting from the trans- and cis-configured 11a-substituted 3-phenyl-2,3,11,11a-tetrahydro[1,3]oxazolo[2,3-b]-[3]-benzazepin-5(6H)-ones 6 and 7. The stereoisomerically pure lactams 6 and 7 were benzylated to give 6-benzyl-substituted products 8 and 9. NOE experiments showed a trans-configuration of the benzyl residue and the residue in the 11a-position indicated that the stereochemistry of the benzylation reaction was controlled by the stereocenter at the 11a-position. Reduction of the benzylated tricyclic benzolactams 8 and 9 with AlCl₃/LiAlH₄ (1/3) yielded the 1,3,4-trisubstituted 3-benzazepines 12 and 13, which were formed stereoselectively with the retention of configuration. Finally, removal of the N-(2-hydroxy-1-phenylethyl) residue by hydrogenolytic cleavage resulted in the formation of enantiomerically pure 1,4-disubstituted 3-benzazepines 14. The σ₁, σ₂, and NMDA receptor affinities of the enantiomerically pure 3-benzazepines 14 and ent-14 were investigated in competitive receptor binding studies. The butyl derivative ent-14c showed a high affinity towards σ₁ and σ₂ receptors, with K_i-values of 26 nM and 41 nM, respectively.     

Heterocycles 35. CaL-B mediated synthesis of enantiomerically pure (R)- and (S)-ethyl 3-(2-arylthiazol-4-yl)-3-hydroxypropanoates

Herein we present the lipase catalyzed synthesis of four new enantiomerically pure (R)- and (S)-ethyl 3-(2-arylthiazol-4-yl)-3-hydroxypropanoates and their butanoates by enzymatic enantioselective acylation of the racemic alcohols rac-1a–d and by ethanolysis of the corresponding racemic esters rac-2a–d mediated by lipase B from Candida antarctica (CaL-B) in organic solvents. In terms of stereoselectivity and activity, both procedures, the acylation and alcoholysis, are successful (50% conversion, E ≫ 200). The absolute configuration of the resolution products was determined by a detailed ¹H NMR study of the Mosher’s derivatives of (S)-1a.     

Synthesis of enantiomerically pure (R)- and (S)-2-ethoxycarbonylmethyl-2-hydroxy-cyclohexanones

Sulfenylation of 2-p-tolylsulfinyl cyclohexanone can be achieved at −78°C with thiosulfonates. The in situ aldol reaction of these compounds with ethyl acetate enolate is highly stereoselective (1,2-asymmetric induction) and yields diastereomeric mixtures of β-hydroxyesters (the configuration of the major one being dependent on the sulfenylating agent) that can be readily separated and transformed into the enantiomerically pure title ketones.     

Studies towards the synthesis of (1R,2S)- and (1S,2S)-1,2-epoxy-3-hydroxypropylphosphonates and (1S,2S)- and (1R,2S)-2,3-epoxy-1-hydroxypropylphosphonates

The trans-configured fosfomycin analogue, diethyl (1S,2S)-1,2-epoxy-3-hydroxypropylphosphonate, was synthesised by the intramolecular Williamson reaction of diethyl (1S,2R)-1,3-dihydroxy-2-mesyloxypropylphosphonate. The cis-analogue was obtained as O-ethyl or O,O-diethyl (1R,2S)-1,2-epoxy-3-hydroxypropylphosphonates, when (1R,2R)-1,3-dihydroxy-2-mesyloxypropylphosphonate or its 3-O-trityl derivative were used as starting materials, respectively. The intramolecular Williamson cyclisations of diethyl (1S,2R)- and (1R,2S)-1-benzyloxy-3-hydroxy-2-mesyloxypropylphosphonates led to diethyl (1S,2S)- and (1R,2S)-2,3-epoxy-1-benzyloxypropylphosphonates, respectively, with the concomitant formation of diethyl (E)-1-benzyloxy-3-hydroxyprop-1-en-1-phosphonate. From diethyl (1S,2S)- and (1R,2S)-2,3-epoxy-1-benzyloxypropylphosphonates, enantiomerically pure diethyl (1S,2S)- and (1R,2S)-1,2-dihydroxypropylphosphonates were obtained by catalytic hydrogenation, while diethyl (1S,2S)- and (1R,2S)-3-acetamido-1,2-dihydroxypropylphosphonates were produced after epoxide ring opening with dibenzylamine, acetylation and hydrogenolysis.     

Asymmetric synthesis of heteroorganic analogs of natural compounds. 2. A convenient preparative method for the synthesis of enantiomerically pure (S)-(-)-o-, m-, and p-fluorophenylalanines and their 2-methylsubstituted analogs

A convenient preparative method for the synthesis of the enantiomerically pure o-, m-, and p-fluorophenylalanines and their -methyl-substituted analogs by means of the alkylation with the corresponding fluorine-containing benzyl chlorides of glycine and alanine in the Ni(II)-complexes of their Schiff bases with (S)-2-N(N-benzylprolyl)aminobenzophenone is proposed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1630–1636, July, 1990.