Disaccharide lactone

In a final step, different mono- and disaccharide lactones (e.g. 5-gluconolactone, glucopyranosyl arabinonic acid lactone etc.) reacted with the synthesized ami-nopolysiloxanes. The reaction lasted 5-6 h, either in refluxing methanol or in ethanol or isopropanol at 70 °C. The reaction gave the expected sugar silicone derivatives quantitatively as yellow or white powders. 

The direct conversion of tri-O -acetyl-D-glucal into the 2,3-unsaturated 1,5-lactone diacetate is reported in Chapter 12 and its use in the synthesis of the disaccharide lactone acetal (5) is outlined in Scheme 1. The key step was glycosyloxyselenatlon which... 

The avermectins are closely related to another group of pesticidal natural products, the milhemycins. First described by Japanese workers, milhemycins were later found to be more abundant in nature than the avermectins (7—12). Both the avermectins and milhemycins are sixteen-memhered lactones, with a spiroketal system containing two six-memhered rings. The principal difference between them is that the avermectins have an a-L-oleandrosyl-a-L-oleandrosyl disaccharide attached at the 13-position whereas the milhemycins have no 13-substituent. Milhemycin stmctures are shown in Figure 2. 

A large series of lactones was thus prepared, with variations in the sugar type, the anomeric configuration, mono- or disaccharides, and benzyl protected lactones. The potential of these lactones is illustrated in the... 

Functionalisation at OH-2 thus led to a series of 1,2-bisfunctionalised platforms prepared from two model lactones, one monosaccharidic (a-gluco) and one disaccharidic (ot-malto). Allylamine and propargylamine were used as model functional appendages due to the wide scope of their possible subsequent chemistry. Their addition on the lactones occurs in high yield and very mild conditions (room temperature, THF, no catalyst,... 

Likewise, the lactol 62, obtained by addition of methyllithium to 2,3,5-tri-O-benzyl-D-arabinono-1,4-lactone, underwent a self-condensation reaction in the presence of BF3 OEt2-MeCN, to afford an anomeric mixture of two C-disaccharides 63 and 64 in 93% yield (66). 

Lactonic disaccharides (such as lactobiono-1,5-lactone) reacted with long-chain primary amines to yield model glycolipids of a new type (111,112). For the formation of JV-substituted aldonamides from aldonic acids and amines, A-V -dicylohexylcarbodiimide was employed as the condensing agent. However, no catalyst was needed in the case of the lactones. 

Hydrogenation of the lactonic disaccharide 168 in the presence of triethylamine and palladium afforded (194) the 3-deoxylactone derivative 181. 

Cuscutic resinoside A (1 tetradecanoic acid, (115)-[[6-deoxy-3-(9-(6-deoxy-a-L-mannopyranosyl)-4-0-[(2/ ,3R)-3-hydroxy-2-niethyl-l-oxobutyl]-a-L-nianno-pyranosyl]oxy]-intramol. l,2 -ester) was obtained from the ethyl acetate-soluble fraction of a methanol extract prepared from the seeds of Cuscuta chinensis Lam. The purification of this compound employed a combination of column and preparative-scale HPLC. The structure was deduced from spectroscopic evidence and acid hydrolysis 14). The degradative process gave convolvuUnolic acid, nilic acid, and L-rhamnose. The sugar components were identified by GC analysis after being converted to their thiazolidine derivatives. This disaccharide has a unique macrocyclic lactone, which is placed between C-1 and C-2 of the first rhamnose moiety. 

Scheme 36 Mono- and disaccharidic carboxymethyl glycoside lactones...

The ease of desilylation may permit the effluent to be collected and then hydrolyzed, and the product (a) transformed into a crystalline derivative, for example, a lactone into a phenylhydrazide,205 or (b) examined by thin-layer chromatography.206 In the case of a glycoside or disaccharide, regeneration of the parent compound permits the configuration of the glycosidic linkage to be determined by enzy-molysis.207... 

Included in this group are avermectins and milbemycins, which are fermentation products possessing a 16-member cyclic lactone, a spirochetal moiety, and a disaccharide unit. Abamycin, ivermectin, doramectin, and eprinomectin are major avermectins available for anthelminthic treatment of livestock, whereas moxidectin is a milbemycin with worldwide acclaim as a cattle anthelminthic (Fig. 4.7). 

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