Furanoid derivatives

Reagents i, BrCH2C02Me, Zn, TmsCi ii, NaBH4, D- or L-tavtaric add iii, BU4NF 

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The methyl ester 107 was obtained by treatment of ammonium KDO with methanol in the presence of an acidic catalyst,79 and it is likely that these esterification conditions (rather than the presence of the ester group of itself) favor the furanoid form. It would be of interest to ascertain whether the methyl ester (111) of KDO, when prepared by Zemplen deacetylation of 70 (see Scheme 31), would also yield furanoid derivatives upon benzoylation with benzoyl chloride in pyridine. 

Interestingly, the furanoid derivative l,4,6-trideoxy-l,4-imino-D-mannitol (76, Scheme 20) was found a potent inhibitor of human oc-mannosidases and was comparable to the parent compound 19 (Scheme 7).210... 

For furanoid derivatives, 2,3-epoxides are readily formed from trans-related groups. Other stereochemical features do not appear to be important, and this reflects the mobility of the orientations on such five-membered rings. Here, eclipsing polar interactions between cis sulfonate and methoxyl groups are not likely to alter much on passing to the transition state and, accordingly, both anomers of methyl 2-O-methylsulfonyl-D-xylofuranoside form the 2,3-anhydro-D-lyxofuranoside on treatment22 with sodium methoxide at 0°. 

The reaction involving 2,3-O-benzylidene sugars was then extended to a study of the behavior of 1,2-O-isopropylidene derivatives.272 Furanoid derivatives 262 and 263 gave, respectively, (+)-(S)-(E)-5-butyl-l-methoxy-3-nonen-2,5-diol (264) (yield 23%) and ( + )-2(R),3(S)-(E)-6-butyl-l,2-dimethoxy-4-decen-3,6-diol (265) (yield 21%). On the other hand, acetal derivatives of the D-arabino (266) and... 

The reaction of sulfuryl chloride with furanoid derivatives has been studied [51,52], and the reaction has been applied to disaccharides, for example, methyl p-maltoside [53] and sucrose [54,55], to yield chlorodeoxy derivatives. 

That bromine atoms can be introduced directly at C-5 of some pyranoid compounds, at C-4 of some furanoid derivatives, and at chemically related centers of certain other monosaccharide compounds was discovered following the finding by Dr. Richard Fumeaux, during his Ph.D. studies in Wellington, that phenyl tetra-O-acetyl-1 -thio-/i-D-glucopyranoside (1) is con-... 

Surprisingly, the 2,3-epoxide ring of pyranoid or furanoid derivatives proved to be highly unreactive toward carbonyl insertion reactions or in rearrangement to ketoses, either when catalyzed by hydrogen cobalt tetracarbonyl or sodium cobalt tetracarbonyl. When moisture was not carefully excluded, preferential hydrolysis of the epoxide ring occurred to afford the diaxial product. 

Although furanoid derivatives in this series have not yet been formally synthesized, it appears that 2,3,5-tri-O-benzoyl-l-deoxy-D-t/ireo-pent-l-enofuranose52 (33) and the D-erythro isomer53 have been produced as by-products during the synthesis of nucleosides from the corresponding 2,3,5-tri-O-benzoyl-D-pentofuranosyl chlorides. 

For conducting acetal condensations under very mild conditions, anhydrous copper(II) sulfate alone, or with the addition of a low concentration (0.1-0.25%) of sulfuric acid, has been used. At room temperature, in the absence of acid, the reaction is allowed to proceed for 3 to 10 days. This procedure is most suitable for furanoid derivatives. It should be mentioned that benzyl 8-D-ribofuranoside was acetonated by refluxing with copper(II) sulfate in acetone for 5 hours. Other catalysts that have been employed include phosphorus pentaoxide, anhydrous... 

HalP has given a full account of early conformational studies of furanoid derivatives by n.m.r. and has shown that although such studies are of undoubted value, over-zealous application of the Karplus equation can perhaps lead to erroneous conclusions. Not surprisingly, therefore, few conformational studies of furanoid derivatives have been reported. 

XIV. Stability of Pyranoid and Furanoid Derivatives Having an Endocyclic,... 

Other Methods - The 2,3-unsaturated compound 26, an intermediate in the preparation of an analogue of the antibiotic PA-48153 C (an immunosupressant) was prepared by deoxygenation of the corresponding 2,3-di-xanthate using diphenylsilane-AIBN. (See also Vol. 25, p. 158, ref. 24 for the preparation of a 5,6-unsaturated furanoid derivative using the same technique). ... 

Lactaranolide derivatives included in Part 12 are produced by silica gel degradation of velutinal esters (7.28, 7.30), methylvelutinal (7.17) or free velutinal itself (for a discussion of these transformations see the chapter on chemical interconversions of Lactarius sesquiterpenes). The compounds upon acidification underwent aromatization to form furanoid derivatives (see Part 18). Under these conditions dehydration reactions took place and also dienes were formed (72). 

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