AbstractAmidification of L‐proline (3) with (+)‐(R,R)‐6 and (–)‐(S,S)‐tartaric anhydride diacetate (7) gave N‐substituted L‐proline derivatives 8a,b, respectively. Acids 8a,b were transformed into diesters 9a,b with MeOH/HCl. Similar reactions with methyl (2S,4R)‐4 and (2R,4S)‐4‐acetoxypipecolate (5) led to bicyclic lactams 14a,b and 15a. Compounds 8a,b were converted into N‐(trihydroxybutyl)pyrrolidine derivatives 8c,d, 10a,b and 11a,b. Methyl (2S,4R)‐20a and (2R,4S)‐4‐acetoxy‐N‐[(2S,3S)‐1,2,3‐trihydroxybutyl]pipecolate (20b) were obtained by displacement of (–)‐(2S,2S)‐2‐O‐benzyl‐3,4‐O‐isopropylidene‐1‐deoxy‐1‐iodothreitol (19) by 4 and 5. Compounds 20a,b were converted into (2S,4R,2′S,2′S)‐21a and(2R,4S,2′S,3′S)‐4‐hydroxy‐2‐hydromethyl‐N‐(2‐benzyloxy‐3,4‐isopropylidenedioxy)piperidine (21b) and finally into unprotected pentols 22a,b. Nonprotected (2S,2′S,3′S)‐11a and (2S,2′R,3′R)‐N‐(1,2,3‐trihydroxybutyl)prolinol (11b), as well as 22a,b, did not inhibit any of the 13 glycosidases assayed. However, a triacetoxy derivative, (2S,3S)‐2,3‐diacetoxy‐4‐[(2R,4S)‐4‐acetoxy‐2‐(methoxycarbonyl)piperidin‐1‐yl]‐4‐oxobutanoic acid (13b) is an inhibitor (IC50 = 157 μM) of α‐L‐fucosidase from bovine kidney.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)