The condensation of the chiral oxazolidinone (I) with 2,4-difluorophenacyl bromide (II) by means of NaHMDS in THF/Et2 O gives the chiral oxirane (III), which is treated with LiOH and H2O2 to eliminate the chiral auxiliary, yielding the carboxylic acid (IV). The cleavage of the oxirane ring of (IV) with 1,2,4-triazole (V) and NaH in hot DMF affords the chiral hydroxyacid (VI), which is submitted to Curtius rearrangement by means of DPPA in hot pyridine to provide the chiral oxazolidinone (VII). The cleavage of the oxazolidinone ring of (VII) by means of refluxing aq. HCl gives the chiral aminoalcohol (VIII), which is condensed with 2-amino-4-chlorobenzoic acid (IX) by means of DCC and HOBt to yield the corresponding amide (X). Finally, this compound is cyclized to the target quinazolinone by reaction with triethyl orthoformate in hot dioxane/NMP.
The condensation of (R)-lactic acid (I) with morpholine (II) gives the corresponding morpholide (III), which is protected at the hydroxyl position with dihydropyran (IV) to yield the tetrahydropyranyl ether (V). The Grignard reaction of (V) with 2,4-difluorophenylmagnesium bromide (VI) affords the chiral 1-propanone (VII), which by a Corey's diastereoselective epoxidation with trimethylsulfoxonium iodide is converted into the oxirane (VIII). The opening of the oxirane ring of (VIII) by means of 1,2,4-triazole (IX) and NaH provides the tertiary alcohol (X), which is treated with pyridine p-toluenesulfonate to give the deprotected diol (XI) as a (2R,3R) and (2R,3S) 4:1 diastereomeric mixture, from which the desired (2R,3R)-isomer (XII) was isolated by crystallization. The reaction of (XII) with Ms-Cl and TEA, followed by cyclization with NaOMe, yields the oxirane (XIII), which is finally condensed with 7-chloroquinazolin-4(3H)-one (XIV) by means of K2CO3 in hot NMP.
Alternatively, intermediate (XIII) can be obtained as follows: Heating of ethyl (S)-lactate (XIV) with morpholine affords amide (XVI), which then reacts with 3,4-dihydro-2H-pyran (A) in the presence of p-TsOH to give protected derivative (XVII). Grignard reaction between (XVII), bromo derivative (XVIII) and Mg turnings in THF yields protected ketone (XIX), which is treated with pyridinium p-toluenesulfonate (PPTS) (THP group removal) and reprotected by means of Tf2O and DIEA to give triflate derivative (XX). Conversion of (XX) into intermediate (XIII) is achieved by reaction with triazolone (VII) and NaH in THF.
Alternatively, derivative (XXIX) can be obtained in an analogous way as its enantiomer (XIX). Diastereoselective epoxidation of (XXIX) with trimethylsulfoxonium iodide and NaH in DMSO provides oxirane (XXX) (3). THP group removal by means of PPTS in EtOH, followed by reaction with 3,5-dinitrobenzoyl chloride (XXXI) and NaHCO3 in CH2Cl2, yields a diastereomeric mixture from which dinitrobenzoate derivative (2R,3R)-(XXXII) is obtained by recrystallization (1). Hydrolysis of (2R,3R)-(XXXII) in MeOH by treatment with aqueous NaOH gives compound (2R,3R)-(XXXIII), which is converted into ester (2R,3S)-(XXXIV) by Mitsunobu reaction with benzoic acid, Ph3P and DEAD in THF. Subsequent debenzoylation of (2R,3S)-(XXXIV) with NaOMe in MeOH affords oxiranyl ethanol derivative (2R,3R)-(XXXV), which is first converted into its triflate derivative by means of Tf2O and DIEA in CH2Cl2, and then into triazolone derivative (2S,3R)-(XXXVI) by reaction with intermediate (VII) and NaH in CH2Cl2/DMF. Finally, oxirane derivative (2S,3R)-(XXXVI) reacts with triazole (XXVI) and NaH in DMF to furnish the desired product.
ER-30346 is synthesized by thiazole ring formation of (2R,3R)-3-(2,4-difluorophenyl)-3-hydroxy-2-methyl-4-(1H-1,2,4-triazol-1-yl)thiobutanamide (I) and 4-bromoacetylbenzonitrile (II) by means of reflux in methanol. The thioamide (I) is obtained with excellent yield from a chiral nitrile (III) by heating with diethyl dithiophosphate in aqueous medium.
The nitrile (III), a chiral key intermediate of this synthesis, can be obtained by two different synthetic routes as follows: Route-a: The key step of this route is ring opening reaction of the trisubstituted oxirane (VII) by cyanide anion leading to the nitrile (III). The chiral oxirane (VII) is synthesized from (R)-lactic acid derivatives as already reported. The reaction of (VII) with diethylaluminum cyanide in toluene or lithium cyanide in tetrahydrofuran gives the nitrile (III) with high yield without any epimerization reaction.
The nitrile (III), a chiral key intermediate of this synthesis, can be obtained by two different synthetic routes as follows: Route-b: The starting material of this route is methyl (S)-3-hydroxy-2-methylpropionate (VIII), which contains one additional carbon between the hydroxyl group and the 2-position carbon of (R)-lactate, the starting material of route-a. The hydroxyl group of (VIII) is protected by triphenylmethyl group. Then, 2,4-difluorophenyl moiety is introduced to give the ketone (X). Direct conversion of the ketone (X) to the oxirane (XIV) by dimethylsulfoxonium methylide, the same condition for compound (IV) in route-a, does not proceed. The oxirane (XIV) having desired stereochemistry is obtained via oxidation reaction. The ketone (X) is converted to the exomethylene (XI) by Wittig reaction. The stereoselective oxidation of (XI) is achieved by means of osmium tetroxide in the presence of 4-methylmorpholine N-oxide to give the diol (XII) in 58% yield after separation of its epimer by column chromatography. After methanesulfonylation of the primary alcohol of (XII), a triazole moiety is introduced and the triphenylmethyl group is deprotected. Then, the primary hydroxyl group of (XVI) is oxidized under Swern oxidation condition to give the aldehyde (XVII), which is converted to the chiral nitrile intermediate (III) by means of heating with hydroxylamine-O-sulfonic acid.