C-Glycosidation

Nikkomycins. The nikkomycins (141—159), isolated from S. tendae are nucleoside-peptide antibiotics (1,4,244,245) as shown in Table 8. Nikkomycins X and Z are stmcturaHy identical to neopolyoxins A and C, respectively. Compound (141) is a competitive inhibitor of chitin synthetase. Two new nikkomycins, nikkomycin pseudo-Z and pseudo-J (158, 159), contain a C-glycosidic bond between C-5 of uracil and C-1 of... 

Fluorogenic compound (56) for transketolase assays has been prepared making use of FruA specificity [123]. Pendant anionically charged chains have been extended from O- or C-glycosidic aldehydes to furnish low molecular weight mimics of the sialyl Lewis X tetrasaccharide such as (SS) (Figure 10.23) [124], Other higher carbon... 

Anew route to 2,5-dihydrofiirans and tetrahydro[3,2-b]furans via ring contraction of pyranoside C-glycosides was reported <96CC1663>. ( )-Homononactic acid and its 8-epimer were synthesized by using a c -selective iodoetherification as the key step (Scheme 21, <96SL777>). 

Beau and Sinay described a method which laid the groundwork for cyanohydrin acetonide alkylations [1]. Their strategy involved alkylation and reductive desulfonylation of glucopyranosyl sulfones 4. In this one-pot procedure, low temperature alkylation and subsequent reductive desulfonylation with lithium naphthalenide generated -C-glycosides with good selectivity >10 1 j3 a) and in moderate to good yield (Eq. 1). 

Initial attempts to effect addition of allyltrimethylsilane with compound 132 under conditions developed in Kishi s C-glycoside work were plagued by epimerization of the acetal center subsequent to the coupling event, providing 133 as a 1 1 mixture of diastereomers (Eq. 21). Boons reported that acetal... 

Deslongschamps P (1993) In Thatcher GJ (ed), The Anomeric Effect and Associated Stereoelectronic Effects. American Chemical Society, Washington, DC, p 26 Recent reviews on C-glycoside synthesis (a) Du Y, Linhardt RJ, Vlahov IR (1998) Tetrahedron 54 9913 (b) Levy DE, Tang C (1995) The Chemistry of C-Glycosides. Elsevier Science, Oxford... 

A recently developed application of the Ramberg-Backlund reaction is the synthesis of C-glycosides. The required thioethers can be prepared easily by exchange with a thiol. The application of the Ramberg-Backlund conditions then leads to an exocyclic vinyl ether that can be reduced to the C-nucleoside.95 Entries 3 and 4 in Scheme 10.6 are examples. The vinyl ether group can also be transformed in other ways. In the synthesis of partial structures of the antibiotic altromycin, the vinyl ether product was subjected to diastereoselective hydroboration. 

Scheme 10.6 gives some examples of the Ramberg-Backlund reaction. Entry 1 was used to prepare analogs of the antimalarial compound artemisinin for biological evaluation. The reaction in Entry 2 was used to install the side chain in a synthesis of the chrysomycin type of antibiotic. Entries 3 and 4 are examples of formation of C-glycosides. 

P2j Z = 2 D = 1.17 R = 0.080 for 3,888 intensities. This is aconfigu-rational analysis of the macrolide antibiotic 23672RP from Streptomyces chryeus. All three sugar residues are pyranoid the conformation of the a-ketose is CX, with Q = 56 pm, 0 = 9° that of the / -D-mycinose (6-deoxy-2,3-di-0-methyl-D-allose) is 4Clt with Q = 59 pm, 0 = 6° and that of the / -L-mycarose (2,6-dideoxy-3-C-methyl-L-riho-hexose) is 1C4, with Q = 53 pm, 0= 177°. The O-5-C-l-O-l-C glycosidic torsion-angles are —71, —87, —83°. The atomic coordinates reported in the paper refer to the opposite enantiomer. 

KATRITZKY POZHARSKII Handbook of Heterocyclic Chemistry, 2nd Edition LEVY TANG The Chemistry of C-Glycosides... 

K. Toshima, N. Miyamoto, G. Matsuo, M. Nakata, and S. Matsumura, Environmentally compatible C-glycosidation of glycals using montmorillonite K-10, Chem. Commun., 11 (1996) 1379-1380. 

K. Toshima, Y. Ushiki, G. Matsuo, and S. Matsumura, Environmentally benign aryl C-glycosidations of unprotected sugars using montmorillonite K-10 as a solid acid, Tetrahedron Lett., 38 (1997) 7375-7378. 

P. Tiwari, G. Agnihotriand, and A. K. Misra, Synthesis of 2, 3-unsaturated C-glycosides by HC104-Si02 catalyzed Ferrier rearrangement of glycals, Carbohydr. Res., 340 (2005) 749-752. 

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