Condensation of acetamide (I) with (R)-epichlorohydrin (II) by means of either NaOH, LiOH or NaOH/benzyltrimethylammonium chloride (BTA-Cl) in H2O yields a mixture of epoxypropane (III) and chloropropanol derivative (IV) that can be converted into the desired product either by direct coupling with isopropylamine (V) in MeOH, or by first reaction of the mixture (III)/(IV) with NaOH to give (S)-(III) and next coupling with (V) as described above (1-3). Alternatively, derivative (S)-(III) can also be obtained by coupling of glycidyl nosylate (VI) with acetamide (I) by means of CsF in DMF.
In this scheme various methods are shown for the synthesis of (S)-atenolol: 1. Treatment of (R)-glycidyl 4-nitrobenzenesulfonate (I) with HCl (either concentrated or with dichloromethane) provides 3-chloropropyl derivative (II), which is then coupled with isopropylamine (III) in dichloromethane to afford 3-chloropropylisopropylamine (IV). Finally, condensation of (IV) with 2-(4-hydroxyphenyl)acetamide (V) by means of KOH in MeOH gives the desired product. Alternatively, derivative (IV) can be converted into (S)-atenolol by its condensation with 2-(4-hydroxy-phenyl)acetonitrile (VI) by means of KOH to yield compound (VII), followed by hydrolysis with HCl at 40 C. 2. Condensation of (R)-glycidyl 3-nitrobenzenesulfonate (VIII) with isopropylamine (III) followed by coupling with acetamide (V) by means of potassium tert-butylate in DMSO provides the desired product. 3. Treatment of (VIII) with HCl affords 2(S)-hydroxy-3-chloropropyl-3-nitrobenzenesulfonate (IX), which is first coupled with isopropylamine (III) to give (IV) and finally condensed with amide (V). 4. Coupling of chloro derivative (IX) with benzyl-protected isopropylamine (X) provides protected derivative (XI), which is then condensed with acetamide (V) by means of KOH in MeOH to give (XII). Finally, compound (XII) is hydrogenated over Pd/C in MeOH for removal of the benzyl group.
The preparation of (S)-atenolol can be performed by resolution of racemic atenolol (I) in different ways: 1. Incubation of (I) with R. arrhizus or G. candidum followed by chromatographic separation, 2. Acetylation of (I), followed by resolution of the enantiomers by incubation with R. arrhizus or G. candidum and subsequent chromatographic separation to afford acetylated derivative (S)-(III). Finally, (S)-atenolol can be recovered by hydrolysis with K2CO3 in MeOH. 3. Treatment of (I) with Lipase PS-D and vinyl acetate or succinic anhydride (which selectively acetylates the nondesired enantiomer), followed by chromatographic separation.
Esterification of p-hydroxyphenylacetic acid (I) with NaHSO4 in refluxing butanol provides butyl acetate derivative (II), which is then subjected to reaction with epichlorohydrin (III) in pyridine to furnish a mixture of epoxypropane (IV) and chloro derivative (V). Treatment of the mixture (IV)/(V) with HCl affords derivative (VI), which is then selectively acylated by means of Lipase Amano PS (LAPS) and vinyl acetate or acetic anhydride/diisopropyl ether to yield compound (S)-(VII). Treatment of the mixture (IV)/(V) with acetyl chloride gives derivative (VIII), which is selectively deacylated using LAPS in butanol/diisopropyl ether to afford derivative (S)-(IX). Coupling of derivative (S)-(VII) with isopropylamine (X) in H2O, followed by removal of the acetyl group with NaOH furnishes derivative (XI) (alternatively, (XI) can also be synthesized by coupling of (S)-(IX) with amine (X)). Finally, conversion of (XI) into the desired product is achieved by treatment with ammonium hydroxide in MeOH.
Treatment of sodium phenoxide derivative (I) with Amberlite IRA-400 (containing quaternary ammonium groups) provides resin (II), which is then coupled with epichlorohydrin (III) in refluxing MeOH to afford arylepoxyether (IV). Finally, (S)-atenolol is obtained by reaction of (IV) with isopropylamine (V) in refluxing MeOH.