Cyclit‐Reaktionen, XI. Umwandlung von Sisamin in Fortimicine

Paulsen, Hans; Schmidt-Lewerkühne, H.

doi:10.1002/jlac.198519850511

Cited by 5 publications

(1 citation statement)

References 16 publications

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“…In each case, the B-D-configurated, 1,3-1inked disaccharide 42 (Scheme 5 ) was the main product, and only traces of its anomer, of (1-4)-disaccharides, or of trisaccharides were observed. The high degree of regioselectiv- ity, favoring glycosidation of the axial OH group is surprising when compared to the preferred glycosidation of the equatorial OH group in 3,4-unsubstituted galactoside derivatives [53]. It is, however, in keeping with the higher nucleophilicity of the OH-C(3) group, as expected from its involvement, as a H-donor, in a H-bond either to the 0-C (l) or to the phthaloyl group.…”

Section: -mentioning

confidence: 99%

ChemInform Abstract: Synthesis of N‐Acetylallosamine‐Derived Disaccharides.

Maloisel¹,

Vasella²

1992

ChemInform

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The protected disaccharide 44, a precursor for the synthesis of allosamidin, was prepared from the glycosyl acceptor 8 and the donors 2628, best yields being obtained with the trichloroacetimidate 28 (Scheme 6). Glycosidation of 8 or of 32 by the triacetylated, less reactive donors 3 8 4 0 gave the disaccharides 46 and 45, respectively, in lower yields (Scheme 7). Regioselective glycosidation of the diol35 by the donors 3 8 4 0 gave 42, the axial, intramolecularly H-bonded OH-C(3) group reacting exclusively (Scheme 5 ) . The glycosyl acceptor 8 was prepared from 9 by reductive opening of the dioxolane ring (Scheme 3 ) . The donors 2 6 2 8 were prepared from the same precursor 9 viu the hemiacetal 25. To obtain 9, the known 10 was de-A-acetylated (+ 18), treated with phthalic anhydride (+ 19), and benzylated, leading to 9 and 23 (Schemes 2 and 3 ) . Saponification of 23, followed by acetylation also gave 9. Depending upon the conditions, acetylation of 19 yielded a mixture of 20 and 21 or exclusively 20. Deacetylation of 20 led to the hydroxyphthalamide 22. De-N-acetylation of the 3-0-benzylated r-o-glycosides 11 and 15, which were both obtained from 10, was very sluggish and accompanied by partial reduction of the 0-ally1 to an 0-propyl group (Scheme 2). The 8-o-glycoside 30 behaved very similarly to 11 and 15. Reductive ring opening of 31, derived from 29, yielded the 3-0-acetylated acceptor 32, while the analogous reaction of the n -D-anomer 20 was accompanied by a rapid 3-0 +4-0 acyl migration (-34; Scheme 4 ) . Reductive ring opening of 21 gave the diol35. The triacetylated donors 38-40 were obtained from 20 by debenzylidenation, acetylation (+ 36), and deallylation (+ 37), followed by either acetylation (+ 38), treatment with Me,SiSEt (+ 39), or CI,CCN (+ 40).

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Section: -mentioning

confidence: 99%