Aldose amides, preparation

Imperial Chemical Industries (ICI) chemists " prepared a novel series of spirocyclic 2,4-oxazolidinediones 243 derived from 7-substituted isatins (Scheme 6.54). The key intermediate a-acyloxy amides 242 were readily prepared from 241 in three steps. Base-catalyzed cyclization of 242 then afforded the target compounds that were reported to be potent inhibitors of aldose reductase. Pfizer chemists approached 5-substituted isatin spirocyclic analogues 243 via a-hydroxy esters 244 that were converted to the corresponding a-carbamyloxy esters 245 in good yield using chlorosulfonyl isocyanate. Cyclization of 245 with potassium ferf-butoxide then produced 243 in acceptable yield (Scheme 6.54 Table 6.10, Fig. 6.20). 

A quinazolodione provides the nucleus for yet another eompound that inhibits aldose reductase. The sequence for the preparation of this agent starts with the isatoate acid (90-1) from 4-chloroantharanilic acid. Heating the compound with the substituted benzylamine (90-2) results in the formation of the ring-opened amide (90-3) with a loss of carbon dioxide. The ring is then reclosed, this time by reaction with carbonyl diimidazole, to afford the quinolodione (90-4). The anion from the reaction of this last intermediate with sodium hydride is then alkylated with ethyl bromoacetate. Saponification of the ester completes the preparation of zenarestat (90-5) [100]. 

Based on lysine as before, single chain derivatives (18) and bicatenar compounds (19) have been prepared by a strategy the inverse of that described earlier [46]. The products (18 and 19) are obtained with higher overall yields than 17. As before, no protection or deprotection steps are needed in this case [46,47]. The synthesis consists of a reaction between two moduU prepared beforehand, one representing the polar head group in the final product and the other the junction modulus. The preparation of this intermediate starts from aldoses or acids derived Irom them that are coupled with lysine in its basic form (Scheme 15). The yields for this step are quantitative. A subsequent amidation reaction with a hydrogenated or perfluorinated fatty acid (Scheme 16) leads to the monosubstituted compounds (18). Esterification of the free acid function of lysine (Scheme 17) yields in a final step the bicatenar structures (19). 

These acids are important precursors in the preparation of sugars with fewer carbon atoms. Oxidative degradation with H2O2 and iron salts (see p. 118) produces an aldose of one less carbon atom thus, D-gluconic acid is converted to D-arabinose, and D-galactonic acid to D-lyxose. Nitriles and amides can also be degraded (see p. 119). 

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