Lactones aldonolactones

A quantitative interpretation of aldonolactone inhibition in terms of an adaptation of the active site to a transition state approaching a planar, glycosyl oxocarbonium ion is made difficult for several reasons. Due to the interconversion between the 1,4- and 1,5-lactones, and their hydrolysis to the aldonic acids, their use is limited to kinetic studies with incubation times of 10 min or less. This was not realized by most investigators prior to 1970. In many cases, only the 1,4-lactone can be isolated its (partial) conversion into... 

The results of inhibition studies with aldonolactones and 5-amino-5-deoxyaldonolactams may be summarized as follows y -D-glycosidases are inhibited by 1,5-lactones and the lactams some 100- to > 10,000-fold better than by the parent aldoses, with Kj values from 200 //Mto <0.1 nM. Al-dono-1,4-lactones are probably no better inhibitors than aldoses or polyols of comparable structure, with the possible exception s of 2-acetamido-2-deoxy-D-glucono-1,4-lactone. 

Aldonolactones are useful starting materials for the synthesis of modified sugars. They have also been used as chiral templates in synthesis of natural products. Some of them are inexpensive, commercially available products or they may be obtained readily from the respective monosaccharides. The purpose of this chapter is to survey the main reactions of aldonolactones. Previous reviews on the subject include articles on gulono-1,4-lactones (1) and D-ribonolactone (2). Methods of synthesis, conformational analysis, and biological properties are not discussed in this chapter. 

Reactions of acetal derivatives of aldonolactones involving the lactone carbonyl group or used as chiral precursors in the synthesis of noncarbohydrate natural products are discussed in later sections. 

Addition of lithiated heterocycles to aldonolactones yields carbon-linked nucleosides (56). Thus, the reaction of 2,3 5,6-di-O-isopropylidene-L-gu-lono-1,4-lactone (9b) or 2,3-O-isopropylidene-D-ribono-l,4-lactone (16a) with various lithiated heterocycles gave gulofuranosyl derivatives 53a-g or ribofuranosyl derivatives 54b,c. Gulonolactols 53a-g and ribonolactols 54b,c were acetylated with acetic anhydride in pyridine to yield their acetyl derivatives. The stereochemistry of compounds 53a-g and 54b,c was discussed in terms of the Cotton effect of circular-dichroism curves of the ring-opened alcohols formed upon reduction by sodium borohydride. The configuration at C-l of 53g was proved by means of X-ray analysis (57,58). 

The Tebbe reagent [//-chloro-bis(cyclopentadienylXdimethylalumin-ium)-/r-methylenetitanium] in its pure, crystalline (70,71) or crude (72) forms has been employed for the methylenation of aldonolactones. Thus, D-ribono- 1,4-lactone derivatives 71a and 71b reacted with Tebbe s reagent to give (70,71) the exo-methylene compounds 72a and 72b. 

The application of lithiumtrimethylsilyl acetate for the C-l elongation of aldonolactones has been examined (73). Although the reagent had been successfully used for the alkenation of lactone carbonyl groups (74), in the case of aldonolactones 10b or 25b only insignificant yields of the alkenes, but 30 - 40% of the lactols 49a or 50a, were obtained (73). However, these lactols, alternatively prepared in good yields by a Reformatsky-type reaction (53,54), were readily eliminated to the desired alkenes by simple treatment with methanesulfonyl chloride-triethylamine at 0°. Thus, from 49a or 50a separable E,Z mixtures (76a and 76b, or 77a and 77b, respectively) were obtained in good yields (73). 

Difluoromethylenation (79,80) of aldonolactones may be readily accomplished by treatment of the lactone derivative with tris(dimethyl-amino)phosphine, dibromodifluoromethane, and zinc in refluxing tetrahy-... 

The acid-catalyzed acetalation of aldonolactones with alkyl acetals of aldehydes or ketones takes place, in some instances, with esterification of the lactone group to give acetal derivatives of alkyl aldonates (11,22). 

Malto-oligosaccharide aldonolactones react with ethylenediamine to give Ar-(2-aminoethyl)aldonamides (113-115), which have been successfully grafted onto carriers via amide linkages. The malto-oligosaccharides were produced by degradation of amylose with alpha amylase. After purification of the oligosaccharides, they were converted into the lactones by hypoiodite or electrolytic oxidation. 

The high-pressure aminolysis of a variety of lactones, including uronic acid lactones, has been described (116). However, the procedure was not applied to aldonolactones. 

Aromatic polyamines react with sugar lactones to give heterocyclic compounds having an attached open-chain polyhydroxyalkyl substituent. Thus, treatment of aldonolactones with o-phenylenediamine afforded (117) 2-polyhydroxyalkylimidazoles (100). 

The procedure was proved to be general for the preparation of protected hydroxy acids from lactones (121). This apparently trivial process is often difficult to carry out, as the attempted derivatization of y or J-hydroxyacids frequently results in relactonization rather than hydroxyl protection. The method was applied to several aldonolactones to produce the corresponding intermediate hydroxyamides. Protection using [(2-trimethylsilyl)-ethoxy]methyl chloride, methoxymethyl chloride, ter/-butylchlorodimeth-ylsilane, or zm-butylchlorodiphenylsilane followed by ozonolysis gave the protected N-(y- or <5-hydroxyacyl)indole derivatives. Mild saponification gave indole and the acetal- or silyl-protected hydroxy acids. 

Sugar lactones react readily with hydrazine to give crystalline derivatives useful for isolation and identification (127). Thus, addition of hydrazine to a reaction mixture containing an aldonolactone facilitates isolation of the product. The lactone may be regenerated from the hydrazide by treatment with nitrous acid (128). The phenylhydrazides obtained on treatment of aldonolactones with phenylhydrazine are also useful for characterization (129,130). 

Pentono- and hexono-1,4-lactones yielded substituted arylhydrazides on treatment with m- and />-tolyl-, m- and p-methoxyphenyl, p-bromophenyl, and p-ethoxycarbonylphenyl-hydrazines (131). It was found that the rate of hydrazinolysis depends on the configuration of the aldonolactone, as well as on the aryl substituent on the hydrazine. 

Because of the activating effect of the carbonyl group, aldonolactone derivatives readily undergo -elimination reactions to yield unsaturated lactones. 

The regio- and stereo-selective functionalization of aldonolactones yields optically active lactones, which are important precursors in natural product synthesis. Concepts such as chiral templates and chirons, derived from carbohydrates, have been ingeniously and widely applied in synthesis (233). Among the commercially available aldonolactones, D-ribono-1,4-lactone is... 

Methyl oxetane-2-carboxylate derivatives (e.g., 284), obtained by ring contraction of aldonolactones, have been employed for the synthesis (279) of the nucleoside / -noroxetanocin [9-(/ -D-eryt/iro-oxetanosyl)adenine, 304] and its a-anomer via an a-chloride obtained by a modified Hunsdiecker reaction. Displacement of chloride by adenine and debenzylation gave 304. The threo isomer of304, /J-epinoroxetanocin (305), was likewise synthesized from D-lyxono-1,4-lactone. The oxetane nucleosides display potent antiviral activity against the human immunodeficiency virus (HIV). 

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