A convergent approach to the synthesis of aprepitant: a potent human NK-1 receptor antagonist

A simple and convergent approach to enantiomerically pure 5-[[2-[1-[3,5-bis(trifluoromethyl)phenyl]ethoxy-3-(4-fluorophenyl)morpholin-4-yl]methyl]-1,2-dihydro-1,2,4-triazol-3-one 1, a potent orally active antagonist of the human neurokinin-1 (NK-1) receptor, is described. The synthetic procedure starts from p-fluorobenzaldehyde to access the racemic morpholinone 2 via a modified Strecker synthesis and utilizes a diastereomeric salt resolution technique to accomplish the synthesis of 1 in enantiomerically pure form and good yield.     

Asymmetric strecker synthesis of alpha-amino acids via a crystallization-induced asymmetric transformation using (R)-phenylglycine amide as chiral auxiliary

[reaction: see text]. Diastereoselective Strecker reactions based on (R)-phenylglycine amide as chiral auxiliary are reported. The Strecker reaction is accompanied by an in situ crystallization-induced asymmetric transformation, whereby one diastereomer selectively precipitates and can be isolated in 76-93% yield and dr > 99/1. The diastereomerically pure alpha-amino nitrile obtained from pivaldehyde (R1 = t-Bu, R2 = H) was converted in three steps to (S)-tert-leucine in 73% yield and >98% ee.     

Practical asymmetric synthesis of aprepitant,a potent human NK-1 receptor antagonist,via a stereoselective Lewis acid-catalyzed trans acetalization reaction

A streamlined and high-yielding synthesis of aprepitant (1), a potent substance P (SP) receptor antagonist, is described. The enantiopure oxazinone 16 starting material was synthesized via a novel crystallization-induced dynamic resolution process. Conversion of 16 to the penultimate intermediate cis-sec-amine 9 features a highly stereoselective Lewis acid-catalyzed trans acetalization of chiral alcohol 3 with trichloroacetimidate 18 followed by inversion of the adjacent chiral center on the morpholine ring. The six-step process for the synthesis of 9 was accomplished in extremely high overall yield (81%) and with only two isolations.     

Process development and large-scale synthesis of NK1 antagonist

A scaleable synthetic route is described to obtain 2-(4-acetylpiperadin-1-yl)-6-[3,5-bis(trifluoromethyl)phenylmethyl]-4-(2-methylphenyl)-6,7,8,9-tetrahydro-5H-pyrimido[4,5-b][1,5]oxazocin-5-one (1, KRP-103) as a neurokinin (NK)(1) antagonist. The key step in the synthesis is the intramolecular cyclization of N-[3,5-bis(trifluoromethyl)phenylmethyl]-N-(3-hydroxypropyl)-4-chloro-6-(2-methylphenyl)-2-methylthiopyrimidine-5-carboxamide (15) which was obtained by amide formation between 4-(2-methylphenyl)-2-methylthio-6-oxo-1,6-dihydropyrimidine-5-carboxylic acid (8) and 3-[3,5-bis(trifluoromethyl)phenylmethylamino]-1-propanol (3). Treatment of 15 with 1,8-diazabicyclo[5,4,0]undec-7-ene provided 6-[3,5-bis(trifluoromethyl)phenylmethyl]-4-(2-methylphenyl)-2-methylthio-6,7,8,9-tetrahydro-5H-pyrimido[4,5-b][1,5]oxazocin-5-one (6). This intermediate (6) is transformed into the candidate compound (1) by two steps; oxidation, and substitution reaction of the resultant sulfone (7) with 1-acetylpiperazine. This synthetic method is free of chromatographic purification and is amenable to large scale synthesis.     

Efficient, diastereoselective chemical synthesis of a beta-mannopyranosyl phosphoisoprenoid

[reaction: see text] Tetrabutylammonium benzyl dihydrophytylphosphate was coupled to S-phenyl 2,3-di-O-benyl-4, 6-O-benzylidene-1-thio-alpha-D-mannopyranoside S-oxide on activation with triflic anhydride in toluene at -78 degrees C to give the corresponding beta-mannosyl phosphate in 56% yield with no detectable formation of the alpha-anomer. Treatment with sodium in liquid ammonia then afforded the unprotected beta-mannosyl phosphoisoprenoid.     

Synthesis of a tetrahydropyran NK1 receptor antagonist via asymmetric conjugate addition

Two asymmetric syntheses of the NK(1) receptor antagonist 1-[2-(R)-{1-(R)-[3,5-bis(trifluoromethyl)phenyl]ethoxy}-3-(R)-(3,4-difluorophenyl)-4-(R)-tetrahydro-2H-pyran-4-ylmethyl]-3-(R)-methylpiperidine-3-carboxylic acid (1) were developed. In both routes, the core tetrahydropyran stereochemistry was established by asymmetric conjugate addition to an alpha,beta-unsaturated ester (6), using an amide of the chiral auxiliary pseudoephedrine. Selective ester reduction then allowed formation of lactone 2 with the thermodynamically preferred trans geometry. The chiral ether side chain (3) was attached by stereoselective acetal substitution. In the first route, the chiral piperidine ester fragment was installed at the end by N-alkylation. In the shorter second synthesis, this piece was appended to the Michael acceptor at the beginning.     

First stereoselective synthesis of 2-deoxy-alpha-D-ribosyl-1-phosphate: novel application of crystallization-induced asymmetric transformation

A first stereoselective synthesis of bis(cyclohexylamine) 2-deoxy-alpha-D-ribosyl-1-phosphate has been achieved. The synthesis features a key crystallization-induced asymmetric transformation (AT) to generate a desired alpha-anomer in 99% yield at a 98.8:1.2 ratio of alpha/beta.     

The first example of a crystallization-induced asymmetric transformation (CIAT) in the Mannich reaction

The novel synthesis of highly enantioenriched N-substituted α-amino-γ-alkyl(aryl)-γ-oxobutanoic acids is described. The process involves the combination of a crystallization-induced asymmetric transformation (CIAT) and the Mannich reaction. The role of retro-Mannich and retro-Michael reactions in the mechanism of the highly stereoselective transformation is also discussed.     

Practical asymmetric synthesis of a selective endothelin A receptor (ETA) antagonist

[structure: see text]. A practical, chromotography-free asymmetric synthesis was developed for the large scale preparation of an endothelin receptor antagonist 2. This synthesis includes a new efficient process for the preparation of 6-bromo-2,3-dihydrobenzofuran, a stereoselective conjugate addition of an aryllithium followed by stereospecific addition of the Grignard reagent of the top aryl bromide, and an aminophosphate-mediated sterospecific intramolecular enolate alkylation, which led to the formation of the five-membered ring bearing three contiguous asymmetric centers.     

A crystallization-induced asymmetric transformation to prepare (R)-4-chlorophenylalanine methyl ester

A second order asymmetric transformation of racemic 4-chlorophenylalanine methyl ester was achieved via salt formation with (2S,3S)-(−)-tartaric acid in the presence of salicylaldehyde to afford the desired (R)-enantiomer of 4-chlorophenylalanine methyl ester in good yield and high enantiomeric purity.     

Stereoselective preparation of a cyclopentane-based NK1 receptor antagonist bearing an unsymmetrically substituted sec-sec ether

A highly efficient synthesis of the potent and selective NK-1 receptor antagonist 1 is described. The key transformation involved the etherification reaction between cyclopentanol 12 and chiral imidate 30 which was catalyzed by HBF4 to initially give ether 14 as a 17:1 mixture of diastereomers and in 75% combined yield. The diastereoselectivity was upgraded to 109:1 by crystallization of the triethylamine solvate 44 which was isolated in 54% yield from 12. Mechanistic studies confirmed that the etherification reaction proceeds through an unprecedented S(N)2 reaction pathway under typical S(N)1 reaction conditions.     

A favourable diastereoselective synthesis of N-(1-S-ethoxycarbonyl-3-phenylpropyl)-S-alanine

N-(1-S-Ethoxycarbonyl-3-phenylpropyl)-S-alanine is prepared by Michael addition of S-alaninebenzylester to ethyl-4-oxo-4-phenyl-2-butenoate in a regio- and diastereoselective fashion and subsequent catalytic hydrogenolysis.     

Protecting-group-free synthesis of a dual CCK1/CCK2 receptor antagonist

In our pursuit of an efficient, protecting-group-free synthesis of the dual CCK1/CCK2 receptor antagonist 1, we have developed chemoselective conditions for sulfonamide formation reaction in pure water and a PhNMe(2) mediated carboxamide formation, both in the presence of a carboxylic acid. Practical synthesis of an unnatural, chiral β-aryl-α-amino acid is also described.     

First diastereoselective chiral synthesis of (-)-securinine

[reaction: see text] A diastereoselective total synthesis of securinine in optically pure form was achieved by employing ring-closing metathesis of the corresponding dienyne compound as a key step.     

Stereocontrolled preparation of a nonpeptidal (-)-spirobicyclic NK-1 receptor antagonist

The synthesis of a spirobicyclic NK-1 receptor (Substance-P) antagonist 1 antipode is described. Retrosynthetic analysis reveals an allylic halide A bearing the cyclopropoxy-substituted aryl group and a 2-phenyl-3-piperidone B. The stereochemistry in the spirobicyclic system bearing three chiral centers is initially set via a highly diastereoselective zinc-mediated coupling of the allylic bromide 23 to the optically active ketopiperidine 3. The remaining benzylic asymmetric center is set by a diastereoselective hydroboration followed by cyclization to the spirobicyclic system.     

Enantioselective synthesis of a dual orexin receptor antagonist

A concise, enantioselective synthesis of the potent dual orexin inhibitor suvorexant (1) is reported. Key features of the synthesis include a mild copper-catalyzed amination, a highly chemoselective conjugate addition, and a tandem enantioselective transamination/seven-membered ring annulation. The synthesis requires inexpensive starting materials and only four linear steps for completion.     

A new nonpeptide tachykinin NK1 receptor antagonist isolated from the plants of Compositae

To find new tachykinin NK1 receptor antagonists from natural sources, we examined the tachykinin antagonist activity in the extracts of approximately 200 species of plants by the use of isolated guinea pig ileum. As a result, we discovered a novel and potent NK1 receptor antagonist in the extract of dried flowers of Matricaria chamomilla L. (chamomile). The structure of the antagonist was established as N1,N5,N10,N14-tetrakis[3-(4-hydroxyphenyl)-2-propenoyl]-1,5,10,14-tetraazatetradecane (tetracoumaroyl spermine, 1a). The Ki values of 1a, estimated from the inhibitory action on the substance P (SP)-induced contraction of the guinea pig ileum and the inhibition of the binding of [3H][Sar9, Met(O2)11]SP to human NK1 receptors, were 21.9 nM and 3.3 nM, respectively. 1a is the first potent NK1 receptor antagonist from natural sources and it has a unique structure of a polyacylated spermine. 1a was concentrated in pollen of Matricaria chamomilla L. and was also found in the extracts of flowers of other four species of Compositae. In addition, we found N1,N5,N10-tris[3-(4-hydroxyphenyl)-2-propenoyl]-1,5,10,14-tetraazatetradecane (2) as a new compound in the extract of flowers of Matricaria chamomilla L., which did not exhibit any tachykinin antagonist activity. A number of related compounds were synthesized, and the structure-activity relationship was studied.     

Efficient synthesis of (±)-8,14-cedranoxide using electrochemical method as a key step

(±)-8,14-Cedranoxide has been synthesized starting from 3,4-dimethoxyphenol, wherein 6-acetoxymethyl-2,6-dimethyl-9-methoxytricyclo[5.3.1.0^1,5]undec-9-en-8,11-dione as a key intermediate has been produced efficiently by means of electrochemical methods.     

A novel diastereoselective synthesis of (Z)-fluoroalkenes via a Nozaki-Hiyama-Kishi-type reaction

A highly diastereoselective and straightforward synthesis for (Z)-2-fluoroallylic alcohols via a Nozaki-Hiyama-Kishi-type reaction with the corresponding bromofluoroolefins was developed, providing an easy access to highly interesting fluorinated synthons.