Anhydro-compounds

Certain carbohydrates are readily converted by acid or heat into anhydro derivatives, and this reaction may complicate both identifi- 

L-Gulose readily forms an anhydride, and in a study on alginic acid, methylated L-guloses were isolated as their anhydrides.88 Other anhydro sugars, such as 3,6-anhydro-L-galactose and its 2-methyl ether, may be found in algae (see, for example, Ref. 412), and, under certain circumstances, 2,3,6-tri-O-methyl-D-galactose may form an anhydride.571 

Lee and Ballou111 investigated five liquid phases for the separation of inositol trimethylsilyl ethers and concluded that QF-1 gave the best results. This column packing permitted resolution of all but the myo-cis pair of inositols. They reported that the order of appearance, regardless of the stationary phase used, is alio, (neo, muco), racemic, (scyllo, epi), and (myo, cis). The order within the parentheses is sometimes reversed, depending on the liquid phase used. Wells and co- 

Hexa-0-(trimethylsilyl)-mj/o-inositol is a solid,112 and this compound and the crystalline per(trimethylsilyl) ethers of scyllo-inositol and myo-inosose-2 have been fully characterized by Loewus,407 who has proposed these compounds as suitable internal standards. The scyllo- and myo-inositols, together with myo-inosose-2, have also been used in a study on the use of electron-capture detectors with trimethylsilyl derivatives.579 

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A development of some promise lies in the dehydration of mannitol and sorbitol to give anhydro compounds. Mannitol can be dehydrated to give 1,4-anhydro-mannitol (XIII) (mannitan) and isomannide, shown to be 1,4 3,6-dianhydro-mannitol (XIV) by Wiggins. Similarly,... 

SE-52 at 160°. Similarly, l,6-anhydro-/ -D-glucofuranose corresponds to /J-D-xylopyranose. These anhydro compounds must be formed in the acid-hydrolysis stage, and they give incorrect values for D-xylose unless their presence is detected 78 this may be done by operating the column at 135°. 

Anhydro compounds can similarly be analyzed from JU2 values. The chemical shift of H-l appears to be the most generally useful parameter, as it lies in the range t 4.95-5.43 when the proton is equatorial or quasi-equatorial, and has a value of r 5.82 for H-I in methyl... 

Methyl 2,3-anhydro compound M.p., degrees [< ]d, degrees Rotation solvent Refer- ences... 

Anhydro compound degrees degrees solvent ences... 

However, saponification of 2-O-p-tolylsulfonyl-L-erythritol or of 2-O-p-tolylsulfonyl-D-threitol did not furnish any 1,4-anhydro compounds, but only the respective tetritol. 

It is probable that the two 1,3-anhydro compounds just described are anhydrides of the same alditol. The compound of Ustyuzhanin and coworkers50 is unequivocally a 1,3-anhydro-D-glucitol derivative, because the hydroxyl groups at C-2, 4,5, and 6 were protected prior to the ring formation. Positive identity of the two would have been achieved by converting the monomethyl ether obtained by Haslam... 

ADP -I- anhydroerythromycin-2 -O-phosphate <3> (<3> conversion to the anhydro compound occurs either during the enzymatic conversion or during the workup [4,5]) [4, 5]... 

A more unusual complication has been encountered that involves the base-catalyzed migration of a p-tolylsulfonyl group between vicinal oxygen atoms (0-4— 0-5). 2,3 6,7-Di-0-isopropylidene-5-0-p-tolylsulfonyl-D-g/ycero-D-gu/o-heptose reacts with sodium methoxide to form (in 16% yield) l,4-anhydro-2,3 6,7-di-0-isopropylidene-a-D-g/ycero-D-a/Zo-heptopyranose. The anhydro compound differs from the original 5-sulfonate in that the configuration of C-4 (rather than C-5) is inverted. Presumably, migration occurs and is then followed by ring closure. Other products are formed, as well.57... 

The derived quaternary salts (e.g. 201) give anhydro compounds (e.g. 202) on treatment with alkali. (3-Pentamethylpyrrolenine (2,3,3,4,5-pentamethylpyrrole) undergoes quantitative conversion to the a-isomer (2,2,3,4,5-pentamethylpyrrole) either on heating (>200°C) or in 1M HC1 at room temperature (71CC1093). Indolenines also undergoes an acid-catalyzed rearrangement (e.g. 203 — 204), known as the Plancher rearrangement. 

The addition of one mole of hydrochloric acid allows the formation of one mole of sodium chloride, which is of advantage in the subsequent addition of halogen, owing to the formation of a sodium salt of the chloromercuric acid, this being more soluble and hence more reactive than the anhydro compound. Acetic... 

The 2//-l,3-oxazine ring was first described by King and Durst202 who revised earlier work of Kohler and Blatt203 and established that the anhydro compounds formed by the action of alkalis on isoxazolium salts are 2H-1,3-oxazines (66) [Eq. (52)]. The same ring system is obtained from an a-cyano-a-bromo ester with triisopropyl phosphite through an... 

It is not to be expected that these two anhydro compounds should be formed in equimolecular proportions, except in the case of a balanced molecule (e.g., certain sugar alcohols) with the sulfonyloxylated carbon atom situated in the middle. 

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