Acylation of ammonium 3-deoxy-n-D-manno-Z-octulopyranosonate (la) leads to the formation of peracetylated 3-deoxy-a-D-manno-2-octulopyranosono-1,5-lactones (3a,b). The proposed structures were confirmed by independent syntheses. The 1,7-lactone was not formed even when only OH-7 was available for lactonisation. Treatment of aldonic acids with acetic anhydride/sodium acetate or pyridine often gives rise to acetylated aldonolactones. lt2 It has been reported that acetylation of methyl-3deoxy-a;D-manno-2-octulopyranosidonic acid gives methyl-4,5,8-tri-O-acetyl-3-deoxy-a-D_manno-2_octulopyranosidono-1,7-lactone in reasonable yield? T.1.c. [EtOAc-cyclohexane (6:4)] of the material formed upon acetylation and esterification (CHINE) of ammonium 3-deoxy-n-D-manno-2-octulopyranosonate (la), consistently revealed the presence of a compound having a lower mobility (Rf .51) than methyl-2,4,5,7,8-penta-Oacetyl-3+%oxy-a-D-m-o-2-octulopyranosonate (2a) (Rf .56), the main product.The elementary composition of this material, obtained crystalline [m.p.123-125"C, [a1:+4.4" (5 1, CHC13)l in about 5% yield after column chromatography [Silica gel 60,Merck,60-230 mesh; EtOAc-cyclohexane (l:l)],was compatible with that of a lactone of a 3-deoxy-2-octulosonic acid carrying 4 acetate groups; the presence of the latter was confirmed by the 1H n.m.r. spectrum (Table ),