Pyranosyl derivatives

Trideoxy-2,3,4-trifluoro-D-galacto- and -gluco-pyranosyl derivatives 391 and 392 have been prepared from l,6-anhydro-4-(9-benzyl-2-deoxy-2-fluoro-/ -D-glucopyranose (385) by use of DAST, through several intermediates, as shown [385 386,10% 387- 388,72% 389 390,90% refl. toluene (for 385) or dichloromethane (for 387 and 389), 24 h]. 

As may be seen from the comparisons of the chemical-shift data for compounds 59 and 60 with those for compounds 61 and 62, two carbon atoms, C-l and C-4, could be monitored in order to distinguish between the two tautomeric and anomeric forms of arabinose. There is an 6-p.p.m. difference between the C-4 signal of arabinose in the pyra-nose and the furanose form. Determination of the chemical shift of the anomeric-carbon atom is, however, not that straightforward, as there is an overlap between the C-l chemical-shifts of arabino-furanosyl and -pyranosyl derivatives (compare the data for compounds 60,61, and 62). The 13C chemical-shift data for C-l, in conjunction with the 13C chemical-shift data for C-4, allow the detection and assignment of arabinose in either tautomeric and either anomeric form. 

Other anions such as nitronate anion,96 or the conjugate base of (3-ketoesters,97 give similar results. Usually, the 1,2-cw-C-glycosyl compound is formed under kinetic conditions. Thus, in the case of the reaction of the GlcNAc derivative 75 with the Wittig reagent Ph3P=CHCOOEt, the a-C-pyranosyl compound 77a is the major product under conditions of kinetic control. Under basic conditions, 77a is slowly epimerized into the more stable (3-C-pyranosyl derivative 77p (Scheme 25). 

Alternatively, pyranosyl radicals can be generated through the reduction of 3,4,6-tri-O-benzyl glucal epoxide with Cp2TiCl2 and manganese metal.136 With the conformationally restricted 1-phenylseleno-D-xylose derivatives 151 and 152 (4Ci conformation) their reaction with Bu3SnCH2 CH=CH2 in the presence of AIBN (Scheme 51) affords the corresponding a-C-pyranosyl derivatives (153) preferentially.137... 

Interaction of the C(l)—X type lone pair on oxygen when the C(l)-—X bond is axial and (b) the sp-type lone pair on oxygen when the C(I)—X bond is equatorial... 

Eigure 2.5 shows the preferred conformations of some pyranosyl derivatives. The examples are chosen both to illustrate the principles by which the conformations are named and also to illustrate the operation of various effects which determine the conformations. The conformations are all necessarily found on the surface of the Cremer-Pople sphere the inter-relations of the various conformations in the northern and southern hemispheres are set out in Figure 2.6. 

Deoxyribonucleosides.—Because of the extreme lability of the poly-O-acyl-2-deoxyglycosyl halides, early attempts to prepare 2-deoxy-ribo -nucleosides by the Fischer-Helferich procedure met with only limited success, in that only the two anomeric 2-deoxy-D-ribo -pyranosyl derivatives of theophylline had been prepared until recently. Almost simultaneously, two groups of workers discovered that, by using acyl groups not normally employed, stable di-0-acyl- 2-deoxy-D-ribo -furanosyl halides (50a and 50b) could be obtained. This discovery led to the direct... 

Conformational studies of glycosyl azides, in particular of pyranosyl derivatives, demonstrate that the azido group behaves like the (9-acetyl group as far as the anomeric effect is concerned. These experimental results show that the dipolar character of the azido group correlates well with the presumed steric (or dipole-dipole or N-N type) and electronic (or conjugative, back-donation or N cr type) interactions governing the anomeric effect. 

Methods for synthesizing anisomycin and pentenomycin, ° and the chemistry and biological transformations of bleomycin and phleomycin have been reviewed.D-Ribo-furanosyl and -pyranosyl derivatives of iV-methyl-iV-nitroso-urea have been prepared as analogues of streptozotocin [2-deoxy-2-(JV-methyl-A -nitrosoureido)-D-glucose] they were reported to be more active against LI 210 leukaemia in mice and less toxic than the parent antibiotic. Likewise N- 2-chloroethyl)-iV-nitrosoureido derivatives of cyclopentane tetrols (35) and cyclohexane tetrols (36) have been synthesized for comparison with streptozotocin. ... 

L-Arabino-furanosyl or -pyranosyl derivatives of 5-thio-substituted indole ... 

D-Lyxofuranosyl imidazoles have been prepared by standard periodate-borohydride chain shortening of corresponding mannofuranosyl derivatives elaboration of the heterocyclic ring from a D-lyxosylamine precursor only gave pyranosyl derivatives. Ribofuranosyl azides have been used to synthesize triazole a and j3-nucleoside analogues by cycloaddition with propynol and 3-chloropropyne, or with methyl 4-hydroxybut-2-ynoate leading to the... 

For example, 342 was converted into 7-oxanorbomenone 351 and subsequently transformed into the polyfiinctional-ized oxanorbornane 352 in six steps (Scheme 13.78). Treatment with HBr/AcOH, followed by MeONa, led to the carbasugar ( )-cyclopheIlitol (354), a potential drug used against HIV and metastasis [123]. In related work, the syntheses of ( )-aminobromocyclitols 355 [124], (3-C-hexo-pyranosyl derivative 356 [125], and dioxabicyclo [3.2.1]-octan-3-one 357 [126], from 342 were reported. 

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