Relative Reactivities of Aminoglycosides and their Synthetic Equivalents in the C-Glycosylation of Aromatics. Synthesis of the Pseudoaglycone (d-C-Glycoside) of the Benzanthrins
作者:Kathlyn A. Parker、Qing-jie Ding
DOI:10.1016/s0040-4020(00)00868-1
日期:2000.12
benzanthrin antibiotics was prepared by a short sequence in which C-glycosylation of dehydrorabelomycin dimethyl ether served as the key step. The use of a 3-azido 2,3,6-trideoxy pyranose as an activated equivalent of a 3-dimethylamino 2,3,6-trideoxy sugar was demonstrated in this reaction.
Highly regio- and stereo-selective C-arylglycosylations of the protected free sugars 1–4, the unprotected methyl glycosides 6–9 and the unprotected free sugars 10 and 11 with 2-naphthol 5 are effectively realized by the combined use of TMSOTf–AgClO4(TMSOTf = trimethylsilyloxytrifluoromethanesulfonate) as a catalytic activator.
An imrpoved practical method for synthesis of aryl C-glycosides from unprotected methyl glycosides and 1-hydroxy sugars
作者:Kazunobu Toshima、Goh Matsuo、Masaya Nakata
DOI:10.1039/c39940000997
日期:——
Aryl C-glycosidations of the unprotected methyl glycosides 9–12 and the unprotected 1-hydroxy sugars 14 and 15 with 2-naphthol 6 using TMSOTf proceed much more effectively than those of the acylated methyl glycosides 4 and 5; the unprotected methyl glycoside 10 is also smoothly coupled with other phenol and naphthol derivatives 25–27 to give the corresponding unprotected o-hydroxyaryl β-C-glycosides
Practical and highly stereoselective aryl and allyl C-glycosidation methods using unprotected sugars as glycosyl donors have been developed. Aryl C-glycosidations of several unprotected 2-deoxy sugars with phenol and naphthol derivatives by the combined use of trimethylsilyl trifluoromethanesulfonate (TMSOTf)-AgClO4 or TMSOTf exclusively gave the corresponding unprotected o-hydroxyaryl beta-C-glycosides which appear in many biologically attractive aryl C-glycoside antibiotics as the key subunit. On the other hand, allyl C-glycosidations of several unprotected glycals with allyltrimethylsilane by TMSOTf afforded the corresponding unprotected and 2,3-unsaturated allyl alpha-C-glycosides in high yields which are versatile synthetic intermediates for the syntheses of optically active natural products.
Convergent total synthesis of vineomycinone B2 methyl ester and its C(12)-epimer
Total syntheses of vineomycinone B2 methyl ester (7) and its C(12)-epimer (epi-7) have been completed. The key reaction for construction of the aryl C-glycoside linkage is the O --> C-glycoside rearrangement starting from D-olivosyl fluoride derivative 11 and anthrol derivative 21, which provides the regio- and stereocontrolled formation of the aryl C-glycoside sector of the target. The combination of Cp2HfCl2-AgClO4 serves as a particularly efficient promoter for this reaction. An extensive model study for attaching the side chain is presented. The Lochmann-Schlosser base cleanly effects ortho metalation of anthracene derivatives 19 and 20. The metalated species can be trapped as stannyl derivatives, from which the corresponding aryllithium species are generated by using n-BuLi or preferably MeLi in toluene. These specific reaction conditions are necessary to suppress the abnormal reaction of RLi reagents at the C(9)/C(10)-positions of the anthracenes. Coupling of the side chain moiety was efficiently carried out by such metalation of anthracene derivative 25 followed by reaction with chiral aldehyde (S)-29. The chiral aldehyde was derived from enantiomerically pure acid (S)-37 obtained by enzymatic kinetic resolution. Deoxygenation of the benzylic alcohol function followed by several steps allowed the total ynthesis of 7. Starting from (R)-aldehyde 29, the same sequence of reactions accomplished the total synthesis of epi-7. The epi series of intermediates provided firm evidence for the stereochemical homogeneity of synthetic 7.