SYNTHESIS AND EVALUATION AS IRREVERSIBLE GLYCOSIDASE INHIBITORS OF MONO(GLYCOSYLTHIO)BENZOQUINONES AND OLIGO(GLYCOSYLTHIO)BENZOQUINONES

The mono(glucosylthio)hydroquinone 2 was prepared by S-glycosidation of 2-mercaptobenzene-1,4-diol and by addition of the acetylated 1-thioglucose 3 to benzo-1,4-quinone (Scheme 1). The second, higher yielding procedure was adopted for the preparation of a range of (glucosylthio)hydroquinones. Addition of 3 to 2-chlorobenzo-1,4-quinone, followed by oxidation gave the 1-thioglucosides 7 and 12 (1.3:1), while addition of HCl to the (glucosylthio)quinone 4 and oxidation gave mainly 12 (Scheme 1). Similarly, the bis(glucosylthio)hydroquinone 33 was obtained from 3 and 4 (Scheme 4), and the (cellobiosylthio)hydroquinone 18 from the thiol 16 and benzo-1,4-quinone (Scheme 2). Addition of the 4-thioglucoside 21 to benzo-1,4-quinone (–> 22) and to 4 was followed by oxidation to yield the mono(glucosylthio)quinone 23 and the disubstituted quinones 24 and 25, respectively (Scheme 3). A mixture 24/25 was also obtained from the addition of 3 to 23. The tris(glucosylthio)hydroquinone 36 was obtained by addition/elimination to the dichloroquinone 29 or the dimesylate 31, which was prepared in a simplified way (Scheme 4). The tetrakis(glucosylthio)hydroquinone 37 was obtained from 3 and chloranil, followed by reduction. The acylated hydroquinones were deprotected (–> 5, 9, 14, 19, 27, 34, and 38), and oxidized to the corresponding quinones (6, 10, 15, 20, 28, 35, and 40). The (glucosylthio)quinones 6, 15, 20, 28, and 35 were tested as time-dependent inactivators of a retaining beta-1,4-glucosidase from Agrobarterium faecalis (Abg), which has a strong exo-glucosidase action (Table 1). Similarly, compounds 20, 28, and 35 were tested with a cellulase from Cellulomonas fimi (Cex) which degrades cellulose and cellooligosaccharides by hydrolysis of a cellobiose unit from the nonreducing terminus. The most effective inactivators for Abg were 6, 15, and 35, which inactivated this enzyme with similar second-order rate constants. (Glycosylthio)quinone 28 was the worst inactivator and did not show normal saturation behaviour. Inactivation of Cex by the (glycosylthio)quinones was 3-500 times slower than that of Abg. The three inactivators 20, 28, and 35 had approximately the same efficacy with Cex, suggesting that they bind to this enzyme in a similar mode. Further, the K-i values observed are very similar to K-m values measured for aryl cellobiosides, implying that they bind at the active site.