Oligosaccharide Analogues of Polysaccharides. Part 8. Orthogonally Protected Cellobiose‐Derived Dialkynes. A Convenient Method for the Regioselective Bromo‐ and Protodegermylation of Trimethylgermyl‐ and Trimethylsilyl‐protected Dialkynes
1996; Wiley; Volume: 79; Issue: 5 Linguagem: Inglês
10.1002/hlca.19960790505
ISSN1522-2675
AutoresAlexander Ernst, Andrea Vasella,
Tópico(s)Enzyme Production and Characterization
ResumoAbstract The cellobiose‐derived dialkynes 14 and 15 were prepared by glycosidation of the acceptor 9 with the thioglycosides 12 (82%) and 13 (85%), respectively. The acceptor 9 was prepared from the known alcohol 2 via the lactone 7 in five steps (48% overall), and the donors 12 and 13 were prepared from the alkynylated anhydroglucose derivative 10 (60% overall). Acetolytic debenzylation of 14 and 15 (→ 16 and 17 , resp.) followed by deacylation of 16 yielded 60% of the cellobiose‐derived dialkyne 18 . Deacylation of 14 (→ 19 ), methoxymethylation (→ 20 ) and trimethylgermylation led to the orthogonally protected dialkyne 21 (69% overall). Protodesilylation of 21 with K 2 CO 3 /MeOH gave 22 (90%), while the Me 3 Ge group was selectively removed with CuBr (19 mol‐%) in THF/MeOH to give 20 (95%). Treatment of 21 with aqueous HCl solution led to 19 (80%). Bromodegermylation of 21 (NBS/AgOOCCF 3 ) led to a mixture of 23 (85%) and 24 (11%). Similar conditions using CuBr instead of AgOOCCF 3 gave exclusively the bromoalkyne 23 (93%). The temperature dependence of the δ values of the OH resonances of 18 in (D 6 )DMSO evidence a strong intramolecular H‐bond between C(5′)O…︁HOC(5).
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