Gentamicin X2 39
. The glycosylation of the fluoride derivatives 43 or 44 with the aprosamine derivative 45 under modified Mukaiyama conditions selectively provided the 1,2-c;>glycosides 46 and 47, respectively, in 40 and 24% yields. Also, the thioglycoside 50, activated by methyl trifluoromethanesulfonate, has been used for the preparation of sorbistin analogs by treatment with the glycosyl acceptor 51, to yield mainly a-glycoside 52  (compounds 43-52).
It should be noted that the addition of aminocyclitol derivatives to glycals catalyzed by boron trifluoride etherate also affords 1,2-c;>aminoglycosides stereo-selectively. Thus, the glycosyl product 54 with an a-anomeric linkage was obtained in 65% yield by addition of the alcohol 53 to the glycal 35  (compounds 53, 54).
In summary, although a large number of naturally occurring aminoglycoside antibiotics and their derivatives have been synthesized, glycosylation methods in this area have not been well developed. This is a major problem especially in 1,2-cis
glycosylation, which often results in a mixture of anomeric products with low yield. In most cases, the modified Koenigs-Knorr condensation is still the most widely used method.
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