Synthese von racemischen Aminozuckersäure‐lactonen: xylo ‐ und lyxo ‐2,3‐Diacetylamino‐5‐acetoxypentan‐4‐olid und ‐2,3,5‐Triacetylaminopentan‐4‐olid

Synthesis of Racemic Aminosugar Lactones: xylo ‐ and lyxo ‐2,3‐Diacetylamino‐5‐acetoxypentan‐4‐olide and ‐2,3,5‐Triacetylaminopentan‐4‐olide Starting with 5‐hydroxy‐2‐penten‐4‐olide ( 1 ), the tricyclic intermediate 4 was prepared via the chloride 2 , the acyl azide 3 , and an intramolecular nitrene addition ( Scheme 3 ). Azide ion opened the aziridine ring in 4 at C(α) to give 5 , which was transformed via 7 into one of the title compounds, the triacetylated diamino‐hydroxy‐lactone 13 ( Scheme 4 ). An alternative conversion of 4 into 13 involved the synthesis of the N ‐acetylaziridine 10 , the opening of the 3‐ring of 10 with N   3 −to form 12 , and a final reductive acetylation ( Scheme 5 ). The third N‐substituent was introduced at C(δ) of 13 by the following sequence: hydrolysis of the AcO group (→ 14 ), mesylation (→ 15 ), substitution by N   3 −(→ 16 ), and reductive acetylation to yield the other title compound, the triacetylated triaminolactone 17 ( Scheme 6 ). Since the ring opening of aziridines by nucleophiles occurs by inversion, the primary products 5a and 12a of the N   3 −reactions as well as the substances derived from them, i.e. 6a , 7a , and 13a ‐ 17a , have the xylo ‐configuration ( a ‐series). Under some of the reaction conditions, the primary xylo ‐products suffered a partial epimerization at C(α) to yield mixtures containing the corresponding lyxo ‐products ( b ‐series): The equilibrium between the xylo ‐ and lyxo ‐isomers was estimated for 5a/5b =1:3, 12a/12b =5:2, 13a/13b =3:1, and 16a/16b =2:1. Since the stereoisomers of the a ‐ and the b ‐series were always separable, the other lyxo ‐products, i.e. 6b , 7b , could be prepared from 5b and 12b .