10.1002/anie.201800169
Angewandte Chemie International Edition
COMMUNICATION
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the 8’S-diastereoisomers (1a-1d) at 76.3-76.8 ppm, and the
reported at 70.3 ppm.
Given the present results, we suggest strongly that the chiral
center at the tertiary C-3’ in the proposed amipurimycin should
be inversed, which was originally assigned according to chemical
transformations that could not lead to the formation of a 2’,3’-O-
acetonide derivative (so as to propose the 2’,3’-trans-diol
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incorrectly.
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In conclusion, the proposed diastereoisomers (1a-1d) and the
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peptidyl nucleoside antibiotic with potent inhibitory activities
against phytopathogenic fungi, have been synthesized for the
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condensation of methyl aminoketones (4a/4b) with 3-oxo-
furanosides (5/18) as key steps to build the branched C9 amino
sugar skeletons, and these C4 and C5 chiral building blocks are
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easily prepared from the abundant amino acids (i.e.,
D- and L-
serine) and pentoses (i.e., -arabinose and -xylose). The N-
L
D
glycosylations, which were found difficult in the previous
studies,[7,9] are realized by the gold(I)-catalyzed glycosylation
reaction with glycosyl o-alkynylbenzoates as donors and N2-Boc-
6-iodo-purine (3) as acceptor in a regio- and stereo-controlled
manner. The successful syntheses of all the eight
diastereoisomers testify the stereo-divergent and robust manner
of the present approach. Nevertheless, discrepancy is found
evident between the NMR data of the synthetic diastereoisomers
and those reported for the natural amipurimycin. While we can
propose confidently that the configuration of the tertiary C-3’ was
erroneously assigned in the literature, the validation of the
structure of amipurimycin has to wait for re-investigation of the
authentic sample. Indeed, this is our current project and we will
provide answer to this riddle in due course.
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Experimental Section
Experimental Details are available in Supporting information
Received: ((will be filled in by the editorial staff))
Published online on ((will be filled in by the editorial staff))
Keywords: amipurimycin, nucleoside, antibiotic,
glycosylation, amino acid, gold.
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