Synthesis and Some Transformations of 2‐Acetamido‐5‐amino‐3,4,6‐tri‐O‐benzyl‐2,5‐dideoxy‐D‐glucono‐1,5‐lactam

Abstract

AbstractThe lactam 21 was obtained in an overall yield of 72% from the hydroxy amide 16 by oxidation with the Dess‐Martin periodinane, acid‐catalysed isomerization of the oxidation products in toluene, whereupon 18/19 precipitated, and reductive dehydroxylation of 18/19 (Et3SiH/BF3 · OEt2; Scheme 1). The amide 16 was obtained by ammonolysis of the N‐acetylglucosamine‐derived lactone 15. Depending on the oxidation method, 16 yielded the keto amide 17, the hydroxy lactams 18/19, and the pyrrolidinecarboxamide 20 in widely different proportions. The pyrrolidinecarboxamide 20 was not reduced under the conditions of the reductive dehydroxylation. Hydrogenolysis of the benzyl‐protected lactam 21 gave the trihydroxy lactam 22, while reduction with NaBH4/BF3 · OEt2 led to the 2‐acetamidopiperidine derivative 24 (Scheme 2). Selective (tert‐butoxy)carbonylation of the lactam 21 (→ 25) followed by NaBH4 reduction and acid‐catalysed solvolysis in EtOH led to the α‐ethoxycarbamates 28/29. Similarly, (tert‐butoxy) carbonylation of 1 (→ 31) followed by reduction to 32/33 and glycosidation yielded the ethoxycarbamate 34. Treatment of the GlcNAc‐derived ethyl glycosides 28/29 with Me3SiCN/BF3 · OEt2 gave the equatorial amino nitrile 30. Under similar conditions, the Glc‐derived glycoside 34 led to the iminooxazolidinone 35. In the presence of a larger proportion of Me3SiCN at 5°, 34 was transformed into the axial, selectively monodebenzylated amino nitrile 36.