The synthesis of n-benzoylristosamine

Sztaricskai, Ferenc; Pelyvás, István F.; Bognár, R.; Bujtás, Gy.

doi:10.1016/s0040-4039(00)72071-5

Cited by 30 publications

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“…Since sugar residue C of the avilamycins l7 was also characterised as the (then unidentified) diacetate (2O),I8 it too must possess the D-arabino-configuration and, in view of close similarities of structure and the absence of decisive chemical evidence, it is not unreasonable to assume that sugar residue C of the everninomicins I 6 9 l 9 also has the same configuration. Both the ketones (12) and (13) afforded nicely crystalline oximes [(21) and (22), respectively], which were transformed into the acetamido-derivatives (23) and (24) Doubtless other antibiotic sugars could be obtained from the ketones (12) and (13) either directly [e.g. L-cladinose 24 (25)] or by manipulation of the configuration and functionality at C-4 after removal of the protecting group at a later stage of the synthesis.…”

Section: Resultsmentioning

confidence: 99%

Convenient syntheses of L-digitoxose, L-cymarose, and L-ristosamine

Brimacombe¹,

Hanna²,

Saeed³

et al. 1982

J. Chem. Soc., Perkin Trans. 1

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Methyl 2,3-0-benzylidene-6-deoxy-4-0-(2-methoxyethoxymethyl) -a-L-mannopyranoside (1 0) and the 4-0-(methoxymethyl) analogue (1 1 ) reacted with butyl-lithium to give the 4-0-substituted methyl 2,6-dideoxy-a-~-erythro-hexopyranosid-3-uloses (1 2) and (1 3), respectively. Appropriate transformations on these keto-sugars afforded practical syntheses of 2,6-dideoxy-~-ribo-hexopyranose (Ldigitoxose) (1 5), its 3-O-methyl analogue (1 7) (L-cymarose), and 3-acetamido-2,3,6-trideoxy-~-ribohexose (N-acetyl-L-ristosamine) .A slight amendment to one of the sugar residues in published structures of the orthosomycin antibiotics flambamycin and avilamycins is indicated.In considering synthetic routes to a number of sugar components of antibiotics, particularly the branched-chain sugars L-evernitrose (1) and L-vancosamine (2), we concluded that methyl 2,6-dideoxy-a-~-ery~hro-hexopyranosid-3-ulose bearing a temporary protecting group at position 4 would serve as a versatile intermediate. Such a compound might be derived from a suitably protected methyl 2,3-0-benzylidene-a-L-rhamnopyranoside by excision of benzaldehyde through the action of organolithium compounds [formally as shown in structure (3)]. Although methyl 2,3-0-benzylidene-4-0-methyl-a-L-rhamnopyranoside (4), . for example, reacts with butyl-lithium in tetrahydrofuran (THF) at -30 "C to give the ketone ( 5 ) in acceptable yield, neither the hydroxylated compound (6) nor the benzyl ether (7) undergo analogous transformations, presumably because either formation of the 4-oxyanion or abstraction of a proton from the benzyl group impedes deprotonation of the dioxolan ring.4 The use of tetrahydropyran-2-yl as a protecting group allows the transformation (8) -+ (9) (40%) to be accomplished with s-butyl-lithium in THF at -30 "C, but protection of the hydroxy-group in this way introduces a new chiral centre. Scattered reports in the literature suggested that either of the protected derivatives (10) or (11) might be better suited for our purpose, although it was known that 2-methoxyethoxymethyl and other ' ethers are cleaved slowly by organolithium reagents at ambient temper at ure. Results and DiscussionEach of the derivatives (10) and (11) was obtained as a distillable mixture of diastereoisomers when methyl 2,3-0-benzylidene-a-L-rhamnopyranoside (6) was allowed to react at room temperature with either 2-methoxyethoxymethyl chloride or methoxymethyl chloride in methylene dichloride containing ethyldi-isopropylamine. Both compounds (10) and(11) reacted with butyl-lithium at -30 "C or below to give, after careful chromatography, the crystalline keto-sugars (12) (41%) and (13) (38%), respectively. In practice we found the methoxymethyl derivative (1 3) much easier to purify. The somewhat modest yields of the ketones (12) and (13), which are comparable to those obtained in similar reaction^,^^^ are offset by the directness of the route (i.e. four steps from Lrhamnose).The usefulness of compounds (12) and (13) in the synthesis of rare sugars is demonstrated by the following exam...

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