Acids and lactones

Pilot experiments to enable an n.m.r. study of the process of la ctonization of sugar acids in solution have been carried 

Similar analysis has shown that all four D-pentano-1,4-lactones 

6-Tetra- -acetyl-D-glucono-1, 5-lactone also adopts the 

The structures of a number of oligosaccharides having L-arabinose at the reducing end have been studied by H- and C-n.m.r. spectroscopy. A series of synthetic methyl 5-glycosides of (i- 4)-Ad -xylo-oligosaccharides of D.P. = 2-6 together with 

The structure of a new disaccharide, glaucobiose (9) from a Chinese drug, Pai-Ch ien , has been established on the basis of its C-n.m.r. sggctra and those of its methyl oi- and -glycosides. 

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Oxidation to Sugar Acids and Lactones. When the aldehyde group of an aldose is oxidized, the resulting compound is an aldonic acid (salt form = aldonate) (11)4. Some aldonic acids are products of carbohydrate metaboHsm. 

Table 2.19 y-Hydroxy-a-amino acids and lactones derived from cycloadducts 491 a-c... 

The oxidation of both linear and cyclic ethers to the corresponding acids and lactones by aqueous H202 as catalyzed by TS-1 and TS-2 was reported by Sasidharan et al. (241) (Scheme 17 and Table XXXV). The titanosilicates exhibited significantly better activity (about 55% conversion) and selectivity (98%) than chromium silicates, although vanadium silicates totally failed to catalyze the reaction. Such conversions are usually accomplished using either stoichiometric amounts of chromium trioxide, lead tetraacetate, or ruthenium tetroxide as oxidants (242) or catalytic amounts of Ru04 in the presence of... 

Tables V-LVII detail H and F shift and coupling information, and Tables LVIII to LXXI incorporate the C-n.m.r. data. The data within this compilation are arranged according to the following outline hexoses prior to pentoses, followed by anhydro sugars, sugar acids and lactones, amino sugars (and their synthetic, A -containing precursors), mono-, di-, and tri-deoxy sugars, branched derivatives, ketoses, polyfluorinated monosaccharides, and, finally, difluorinated amino sugars. Within this compilation, and even within each table, pyranoid derivatives are listed prior to their furanoid counterparts, hexoses prior to pentoses, functionalized prior to deoxy compounds the arrangement within each sub-table is made alphabetically.

For the separation of crystalline diastereomeric p,n-pairs, the same principles as for enantiomers are followed. Similar to the chromatographic resolution of enantiomers, the scale may vary significantly, but, in general, the separations of diastereomeric pairs are more reliable. For example, acids and lactones which may be separated via their phenylglycinol amide derivatives by MPLC on silica gel. Some examples with their derivatives and chromatographic method used for separation arc listed in Table 10. 

In the carbohydrate series, the acids encountered are aldonic, aldaric, uronic, or saccharinic acids. Often, these acids are readily transformed into their lactones or methyl esters, and it is as derivatives of these that they are commonly studied. Table VIII (see p. 136) records examples in which derivatives of such acids and lactones have been subjected to gas-liquid chromatography. 

Chiral oxazolines have been used in the chiral-selective assembly of carboxylic acids and lactones. The chiral oxazoline (407) was prepared using a commercially available chiral aminodiol. Metallation at -78 °C gave a lithiooxazoline which was alkylated with a variety of alkyl halides to afford on acid hydrolysis a-alkylalkanoic acids (409) of the (S)-configuration (72-82% e.e.). The methoxyamino alcohol released during the hydrolysis could be recycled to produce again the chiral oxazoline (Scheme 91) (79PAC1255). 

The addition of an allyl metal to a-amino aldehydes has been used by Vara Prasad and Rich (Scheme 12)J23l After the addition step, the allyl group is oxidized to a carboxylic acid and lactonized. Then, the a-carbon of the lactone is alkylated stereoselectively. These investigators also systematically examined the addition reaction to determine its diastereo-selectivity. The highest diastereoselectivity was obtained when allyltrimethylsilane was used in the presence of tin(IV) chloride. An increase in the steric bulk of the protecting group and of the side chain also resulted in a better diastereoselection. Alternatively, Taddei and co-workers 24-26 used a 2-(halomethyl)allylsilane and the side chains were introduced by nucleophilic substitution of the halogen (Scheme 13). 

The controversy centered, on the structure of the free acids which were obtained from the esters by hydrolysie,and the question was not easily settled for apparently the reactions of the compound could be interpreted in two ways. In perfect accord with the unsaturated formula the acid added hydrobromic acid easily1 to give a product wnich was shown to be CKatJr-CHa-CH< ) ) on heating the vlnaconic acid", carbon dioxide was evolved and a monobasic acid and lactone CHa - CH - CHs were obtained. Tne forma-... 

If the dibromo acid is treated with alkali under milder conditions, for example with 1 m sodium hydroxide solution at 20-25 °C for 0.5 hour, the intermediate y-hexylaconic acid (m.p. 123-125 °C) can be isolated after acidification. The infrared spectrum shows absorptions at 3110cm-1 (C—H stretch, alkene), 1715 and 1745 cm-1 (0=0 stretch of carboxylic acid and lactone) and 1630 cm (0=C stretch). 

The oxidation products are divided into two principal categories, namely, acids (and lactones) and neutral compounds. 

AT, o-HAT, p-HAT (acid and lactone form) Human serum Positive ion electrospray tandem mass spectrometry LOQ 0.5 ng/ml HPLC-ESI-MS deuterium labeled analog was used as internal standard... 

J. Mohammed, O. Zheng, C.C. Bang, T. Deborah, Quantitation of the acid and lactone forms of atorvastatin and its biotransformation products in human serum by high-performance liquid chromatography with electrospray tandem mass spectrometry, Rapid Commun. Mass Spectrom. 13 (1999) 1003-1015. 

Scheme4.92. Reaction of 2,3-epoxycarboxylic acids and lactones with halides [393, 394],...

Although many solvent developers are applicable to the acids and lactones, those containing acid have been favored. Acidic solvents, by a swamping effect, 129 suppress ionization of the sugar acids and thus prevent streaking of the acid spots.82 27 Otherwise, the ionized acids would be preferentially held by the stationary aqueous phase in the chromatogram, or would be adsorbed with resulting low RF values. In basic... 

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