Furanoid compounds

2 Furanoid Compounds.- N.O.e. experiments have shown that the anomeric configuration of C-furanosldes can be determined by this method. 

Both anomers of tri- -benzyl-D-ribofuranosyl fluoride with 2-trimethylsilyloxypropene and boron trifluoride gave a very high yield of the acetone compound and both anomers of the 

The aryl glycosides (62) have been obtained using arylmagneslum bromides with acylated pentofuranosyl halides.Intramolecular reaction of substituted-benzylated glycosyl acetates in presence of 

Noyori, K.Hayashi, and S.Hashimoto, Organosilicon Biorganoailicon Chem., [Proc. Int. Symp. Organosilicon Chem.], 7th, 1984 (Pub. 1985), 213 (Chem. Abstr., 1986, 129 944). 

Kunz cind W.Pfrengle, J. Chem. Soc., Chem. Commun., 1986, 713. 

2 Furanoid Compounds.—An n.m.r. proton-proton coupling constant method has been applied to the anomeric configurational determination of C-glycosidic analogues of 2-deoxy-D-e/yr/iro-pentofuranosides.  

A novel Reformatsky reaction using ethyl bromoacetate-zinc-titanium tetrachloride has been applied with l-0-acetyl-2,3,5-tri-0-benzoyl-p-D-ribose to give the 3-linked product (159). Compound (160), obtained by use of a Grignard reagent and a glycosyl chloride, has been made as a nucleoside analogue and incorporated into oligonucleotides for studies of duplex stability.  

5-Tri-(9-benzyl-D-arbinose with magnesium phenates gave o-hydroxyphenyl C- 

Several C-glycosides have been produced by elaboration of simple anomeric 

Yamada, M.Nishizawa, Tennen Yuld Kagobutsu Toronkai Koen Yoshishu, 1989, 31, 38 Chem. Abstr., 1990,112, 217 401). 

2 Furanoid Compounds.- Reaction of substituted D-rlbofuranosyl fluorides with silyl enol ethers and allyl trimethylsllane gives mainly a-C -glycosides. Similar reaction of 2,3,5-trl-O-benzyl- 

Various other means of obtaining furanosyl C-glycosides have been described. The fructofuranoslde (65) afforded the C-allyl compound (66) from which a- and 3-D-fructofuranosyl C-glycosides were produced compound (67), on treatment with N-bromosuccinl-mide, gave the product of 0-5 participation (68) and the 2-0- 

The alkene (7 ), produced by Wittlg chemistry from 2,3,5-tri-0-benzyl-D-arabinose, reacts with electrophiles to give the B C glycosides (75) and the phosphonate (76) from which the D-arabinose phosphonate isostere (77) of D-arabinose 1,5-diphosphate was made. 

Reaction of 2,3-0-isopropylidene-D-ribose with Wittig reagents gives mainly B-products under kinetic control and a-products 

Re xgen s i-,, U, mtUi-base iu, EtO EtOH iv, Ph3p=C.HCOtre 

Wilhelm, S.K. Chatterjee, B. Rattay, P. Nuhn, R. Benecke and J. Ortwein, Liebigs Ann. Chem., 1995,1673. 

Hashimoto, K. Umeo, A. Sano, N. Watanabe, M. Nakajima and S. Ikegami, Tetrahedron Lett., 1995,36, 2251. 

Mickeleit, T. Weider, K. Buchner, C. Geilen, J. Mulzer and W. Reuth, Angew. Chem. Int. Ed. Engl., 1995,34,2667. 

Moitessier, F. Chretien, Y. Chapleur and C. Humeau, Tetrahedron Lett., 1995, 36, 8023. 

Panintrarux, S. Adachi, Y. Araki, Y. Kimura and R. Matsuno, Enzyme Microb. 

Mukaiyama, K. Takeuchi, S. Higuchi and H. Uchiro, Chem. Lett., 1996,1123. 

Alonso, N. Khiar and M. Marto-Lomas, Tetrahedron Lett., 1996,37, 1477. 

Zapata, B. Bemet and A. Vasella, Helv. Chim. Acta, 1996,79,1169. 

Rodriguez, A. Gomez, F.Gonzalez, E. Barzana and A. Lopez-Munguia, Appl. Biochem. Biotechnol, 1996,59,163 Chem. Abstr., 1996,125,58 886). 

Shimizu, Y. Ito, Y. Matsuzaki, H. lijima and T. Ogawa, Biosci Biotech Biochem, 1996,60,73. 

The anomeric phosphonates (6I), which are analogues of the glycosyl 1-phosphates, have been made using a Wittig reagent 

Direct condensation of l- -acetyl-2,3,5-tri-0-benzoyl-6-D-ribo-furanose and allyltrlmethylsilane in the presence of zinc bromide or boron trifluoride gives the anomers (62) in the a 6 ratios of 4 1 and 7 1, respectively, and analogous reaction of 1-hexene in the presence of tin(IV) chloride gave not just the C-glycosides (63) but also chlorinated adducts. The use of trimethylsllyl triflate avoids this problem, but only 20 yields are obtained. On ozonolysls, the alkenes (63) gave glycosylethanals from which other 

Several simple anomerlo substituents In -glycosides have been 

Synthesis of 3 6-anhydro-2-deoxy-4,5-0-isopropylldene-D-allo-heptonic acid lactone (66) from D-ribose has been achieved in 31 overall yield via the Wlttig-derived Intermediate (67).  

Whereas methyl 2-amlno-2-deoxy-oi-D-glucopyranoside with sodium nitrite in anhydrous acetic acid gave mainly the 2,5-anhydro-D-mannose derivative (68), the 0-tetra- -acetate of the same sugar and 2,3,4,6-tetra-0-acetyl-3-D-glucopyranosylamine gave mainly the 

3-0-Isopropylidene-6-0-trityl-P-ribose treated with phosphonate (168) gave the C-ribofuranosylglycines (169) in high yield in a one-pot procedure. The (S)-isomer was characterized by X-ray cystallographic methods.  

A further one-pot synthesis gives tri-0-benzoyl-p-J -ribofuranosyl cyanide in 86% yield, and a 2-deoxy analogue was made using (Tanodiethylaluminium.  

The diene (170) has been used to produce racemic compounds of the C-gItycofuranosyl type (e.g. 171) and a new synthesis of muscarine (a further C-gfycofuranoside) from L-rhamnose is referred to in Chapter 24. 

Konradsson, C. Roberts and B. Fraser-Reid, Reel Trav. Chim. Pays-Bas, 1991, 770, 23 (Chem. Abstr., 1991,114,143 828). 

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The conformation that a furanoid compound will adopt in the crystal is not readily predicted. A furanoid compound can adopt one of four envelope conformations in which C-2 or C-3 is endo or exo, namely, 2E, E2, 3E, and E3 less commonly, it may adopt a twist conformation. The energy difference between the four common envelope conformations may be so slight that other effects predominate in determining the conformation that the compound will adopt, both in the crystal and in solution. Such effects include those caused by hydrogen bonding, solvation, and close contacts with an aglycon. 

Although exact mechanisms have not been described for the formation of other furanoid compounds through amine-carbohydrate interactions, probably many of the 32 furans described by Ohloff and Flament (23) from meat aroma mixtures are from this source. Shiba-moto (24) described many of the same components from mixtures producing meat odors. 

Pyranones, furanones, and related compounds (6, 7). Structurally these substances are generally cyclic ethers, mainly furanoid compounds. They are found in condensates from carbohydrates that have been subjected to browning reactions. 

Relevant pyranoid and furanoid compounds (with the exception of the furanoid 3-enes that, as enol ethers, are noted in Section IV. 1) have isolated double bonds in the sense that they are not components of vinyl ethers. In consequence their chemistry is distinct from that of the glycals and their derivatives in particular, their addition reactions are seldom regioselective as are those of the glycals. 

An illustration of the potential value of 2,3-unsaturated furanoid compounds, particularly in nucleoside synthesis, is the preparation, by way of an epoxy intermediate, of a crystalline compound claimed to be ethyl 3-amino-3-deoxy-DL-arabinofuranoside from racemic 2-eth-oxy-2,5-dihydro-5-(tetrahydropyranyloxymethyl)furan (41, R = OEt,... 

Alkyl fructosides have remained rather inaccessible and have, consequently, received only scant attention. We have found that the reaction of fructose and alkyl alcohols can be achieved by taking special precautions. Initially, furanoid compounds are formed which are in the course of the reaction partly transformed into the /l-fructopyranoside. Separation of the products by preparative HPLC allowed us to study the esterification of structurally homogeneous compounds . 

In contrast to the stability of furanoid systems having an exocyclic, enolacetal double bond are the less stable (more reactive) furanoid compounds possessing an endocyclic enolacetal linkage. Todd and co-workers and Vizsolyi and Tener reported the instability of the 3,4-unsaturated 3-deoxypentofuranoid conjugates obtained by alkaline j3-elimination of phosphate from terminally oxidized, nucleotide model compounds such as 240. The unstable, endocyclic enolacetal conjugates (241) were transformed by a second elimination reaction into the more-stable furan derivatives (242). The extent to which the stability of the... 

C-4 linked carboxylate group of the furanoid compound (241) bearing the endocyclic enolacetal linkage was influenced was not ascertained. 

To obtain relative response factors and retention times, the pure compounds were fed and then eluted, although some of them, such as cellobiosan and 1,6 anhydro-3-D-glucofuranose, had to be synthesized in-house [13]. Confirmation of compound identification was obtained by GC-MS [Hewlett-Packard 5970 Mass Selective Detector coupled to 5890A Gas Chromatograph]. For GC-MS analysis, sugars and anhydrosugars were first trimethylsilylated to the corresponding ethers. Small amounts of simple phenols and of furanoid compounds were also detected by GC-MS in the water soluble fraction. These components were not quantified by HPLC. 

Correlations for Pyranoid and Paranoid Forms of Aldose and Ketose Derivatives. For aldo- and ketofuranose derivatives, Barker and Stephens (1954) found absorption frequencies at the following mean values type A, 924 cm and type D, 799 cm F Type A absorption was not distinguishable from types 1 or 2b of aldopyra-noses, and therefore has no diagnostic value for differentiating between furanoid and pyranoid aldoses. Most of the furanoid compounds also displayed type B absorption at 879 cm and type C absorption at 858 cm . It has been observed (Tipson et al, 1967 Tipson et al, 1959 Tipson and Isbell, 1961a) that these correlations are, for the most part, restricted to the compounds they studied, and cannot be extended to have a wider diagnostic applicability to related compounds. 

The 5,6-unsaturated compound (51), which is also the methylene derivative (52) prepared from the corresponding D-gluconolactone tetraether with Tebbe s reagent, underwent the reactions Illustrated in Scheme 19. A set of furanoid compounds (53) have been found... 

Furanoid Compounds.—As has become usual, a range of methods have been applied to the synthesis of compounds of this series. Scandium perchlorate, an unusual Lewis acid catalyst, catalysed the reaction of 2,3,5-tri-O-benzoyl-P-D-ribopyranosyl acetate and a-(trimethylsilyloxy)styrene to give the benzoylmethyl C-furanosides in very high yield with 94 6 selectivity in favour of the a-anomer. In parallel work the analogous benzylated ribofuranosyl... 

Furanoid Compounds.-Reaction of Meldrum s acid, which was mentioned at the beginning of the last section, with L-arabinose and n-mannose gives, in DMF in the presence of triethylamine, compounds 140 and 141 in 47% and 39%, respectively. In the case of the latter compound the manno-v ovaet, formed without epimerization, was produced in 11% yield. Treatment of the corresponding free sugars with methylenesulphinyl ylid... 

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