Isopropylidene derivatives hydrolysis

O-isopropylidene derivative (10) was then phosphorylated with phosphorous oxychloride to form the phosphate ester (11) from which the protecting groups were removed by mild acid hydrolysis. The 3-phos-phate (15) was obtained by phosphorylating the 4,6-benzylidene derivative (13) of the same glycoside with phosphorus oxychloride, followed by hydrolytic removal of the protecting groups, from the ester (14) thus obtained. 

Deoxy-D-jcylo hexose 6-(dihydrogen phosphate) (21) has also been synthesized (2) the reaction sequence makes use of 3-deoxy l 2,5 6-di-O-isopropylidene D-galactofuranose (16), a compound that can be easily prepared from D-glucose (2, 60). The mono-isopropylidene derivative (17) formed by partial hydrolysis of the di-ketal is converted into the 6-tosylate (18) by reaction with one molar equivalent of p-toluenesulfonyl chloride. From this the epoxide (19) is formed by reaction with sodium methoxide. Treatment of the anhydro sugar with an aqueous solution of disodium hydrogen phosphate (26) leads to the 6-phosphate (20)... 

Selective removal of one isopropylidene group from a diacetal may be achieved by a variety of procedures, most of them involving protic or Lewis acids.100 Particularly common is the hydrolysis of the acetal engaging of the primary position of di-O-isopropylidene derivatives. Bhaskar et al,101 studied the selective deprotection of di-O-isopropylidene acetals derived from D-glucose, D-xylose, and D-mannose, using acid zeolites and montmorillonite K-10. When 102 was submitted to acid hydrolysis in aqueous methanol, the best yields (85—96%) for the monoacetal 105 were obtained when H-beta and HZSM-5 zeolites were employed as catalysts (Scheme 24, Table IV). HY zeolite proved to be ineffective, whereas the yield obtained for the montmorillonite K-10-catalyzed reaction was low (22%). The zeolites found most effective were then used for the hydrolysis of the diacetal 103 and 104, providing excellent yields for the desired corresponding monoacetals 106 and 107. 

The crystalline tri-0-isopropylidene-(2-hydroxy-L-x2/Zo-hexose) prepared from L-gulosone closely resembles the corresponding o-arabino-hexose derivative7 (p. 73) and is believed to have a similar structure.193 On graded hydrolysis, it forms a di-O-isopropylidene derivative which may be characterized as the crystalline diacetate. 

Studies on the rates of hydrolysis of di-O-isopropylidene derivatives of ketoses indicated that the relative order of stability of 2,2-di-methyl-l,3-dioxolane rings is in the order cis-fused to a furanoid ring > sptro-fused to a pyranoid ring > cts-fused to a pyranoid ring > sptro-fused to a furanoid ring.8 Thus, partial hydrolysis of l,2 3,4-di-0-isopropylidene-/3-D-en/fhro-2-pentulofuranose (1) to the 3,4-acetal (2)... 

Bell114 has suggested that the very ready hydrolysis of a -diisopro-pylidene-D-fructose might possibly indicate a furanose structure, namely, that a-diisopropylidene-D-fructose is l,2 4,6-diisopropylidene-D-fructo-furanose. Hydrolysis would have to be accompanied by change in the size of the ring since the structure of the mono-isopropylidene derivative is, without doubt, pyranose. In this connexion, however, it should be... 

These isomeric acetonated nitrodesoxy sugars could not be separated by fractional crystallization but a selective re-acetonation of the mixture gave mainly the di-isopropylidene derivative of the nitrodesoxy-L-idose, which then could be separated readily from the unchanged mono-iso-propylidene nitrodesoxy-D-glucose. Hydrolysis of the isopropylidene substituents with dilute acid then gave, respectively, 6-nitro-6-desoxy-L-idose and 6-nitro-6-desoxy-D-glucose. 

Dipolar cycloaddition of the sodium salt of cyanoacetamide or mal-ononitrile to the acetonide of racemic or optically active l-azido-2,3-dihydroxypropane 290 afforded the intermediate triazoles 291, which were converted directly to the 2-substituted 9-(2, 3 -dihydroxypropyl-8-azahypoxanthines 294 and 8-azaadenines 295 by treating with a suitable ester or nitrile to give the isopropylidene derivatives 292 and 293, respectively, followed by acid hydrolysis. The percentage of racemization was determined by NMR with the Europium shift reagent [Eu(tfc)3] (91JHC1351) (Scheme 58). 

In the field of natural red algal galactans, MS was used for the first time in the structural analysis of odonthalan.353 Galactose and 6-O-methylgalactose, the hydrolysis products of the polysaccharide, were separated by column chromatography and identified by MS in the form of their di-O-isopropylidene derivatives. Cyclic derivatives of this type had been shown previously to be especially suitable for mass-spectrometric characterization of the structure and (in certain instances) stereochemistry of monosaccharides.349,354 A combination of GLC and MS was also used for identification of methyl 4.6-O-0 -methoxycarbonylethylidene)-D-galactosides (as their trifluoroacetates) in the methanolysis products of Ji-carrageenan from Petrocelis middendorfii,355... 

Acetamido-5-deoxy-D-ribose has been synthesized from benzyl 2,3-O-isopropylidene-)3-0-ribofuranoside through the sequence of the 5-0-p-tolylsulfonyl, 5-azido, and 5-acetamido derivatives. Hydrolysis of benzyl 5-acetamido-5-deoxy-2,3-0-isopropylidene-j8-D-... 

The selective hydrolysis of acetyl groups, led in methanol in presence of concentrated sulphuric acid, gives the a,P unsaturated methyl ester 13e. Therefore the two hydroxyls at C-3 and at C-4, in sin position each other, are protected by means of formation of isopropylidene function, doing react the methyl ester 13e with 2,2-dimetiioxypropane in acetone in presence of catalj tic quantity of strongly acidic resin, so obtain the 3,4-O-isopropylidene derivative 13f. 

The isopropylidene derivatives 66 (Refs. 418, 419, 424, and 497) and 68 (Refs. 415, 419, 424, and 497) are usually prepared from 62 or l,6-anhydro-2,3-0-isopropylidene-/3-D-mannopyranose by using an oxidation-reduction sequence, such as 62—>65—>66 or 78— 68 on hydrolysis, the acetals yielded415 419,424,497 1,6-anhydro-/3-D-talopy-ranose (67). This process also permits the preparation of various specifically deuterated 1,6-anhydro-O-isopropylidenehexopyranoses... 

Hydrolytic removal of acetals can be selective, as in the well-known production of 1,2-isopropylidene ot-D-glucofuranose from mild acid-catalysed hydrolysis of l,2 5,6-diisopropylidene ot-D-glucofuranose. °° The difference in reactivity of the two isopropylidene derivatives lies in the differing stabilities of the oxocarbenium ion intermediates. Under acid-catalysed conditions, a cyclic ketal with different electron demand at the alcohol sites will first open to give the most stable oxocarbenium ion leaving group ability is not an issue... 

Phosphorylation of ribofuranosyl nucleosides7 Japanese chemists found that phosphoryl chloride is an excellent catalyst for the conversion of ribonucleosides into the 2, 3 -0-isopropylidene derivatives. These, on addition of pyridine, are esterified at the primary 5 -position. Aqueous hydrolysis then gives the nucleotide, The method can be used for a single-step conversion of ribonucleosides into ribonucleotides by using a combination of POCL, acetone, and pyridine without isolation of the isopropylidene derivative. 

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