Other Ester Derivatives

Fusion of 5,6-0-carbonyI-l,2 3,4-di-0-isopropylidene-D-mannitol (129) with nitrogen heterocycles e.g. pyrimidines, purines, and cyclic imines) in the presence of catalytic amounts of tetraethylammonium bromide gave the corresponding 1- 

4- Tetra-0-acetyl-5,6-0-carbonyl-D-mannitol gave 2,3,5,6-tetra-0-acetyl-l,4-anhydro-D-mannitol under identical reaction conditions, via an intermediate 

Diethylborylation of L-rhamnose with activated triethylborane gave the a-pyranose tetraboronate (130), which afforded a mixture of products, containing 

The use of mass spectrometry for identifying sulphated sugars is discussed in Chapter 21, and the nitration of nucleosides and nucleotides with nitronium tetra-fluoroborate is noted in Chapter 19. 

The treatment of nucleosides with N,0-diacetyl-hydroxylamines in water or acetone causes alkylation of the bases, whereas in phosphate buffer at the same pH adenosine and guanosine are acetylated on the ribose units. 

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The preparation of the reagent of Step 1 and other ester derivatives is described (3) and illustrated in Eq. 1 ... 

Recently, the isocyanide 53 was converted into the U-4CR products 54 (Scheme 16) these can be cleaved under mild conditions to give the products 55 and 56.P°1 In an analogous manner, many other ester derivatives of 53 could be employed. The chemistry of 53 and its related derivatives provides new preparative possibilities in peptide chemistry. 

Cleavage ofpropargyl esters. With the use of this salt, the selective removal of the propargyl group is possible without affecting other esters derived from allyl, benzyl, and alkyl alcohols. 

Other ester derivatives that are available include hydrocortisone cypionate [21-(3-cyclopentylpropionate) ester], hydrocortisone butyrate (1 7a-butyrate ester), hydrocortisone buteprate (17a-butyrate, 21-propionate esters), hydrocortisone valerate (17a-valerate ester), hydrocortisone sodium succinate (21-sodium succinate ester), and hydrocortisone sodium phosphate (the 21-sodium phosphate ester) (Fig. 33.10). The water-insoluble hydrocortisone cypionate is used orally in doses expressed in terms of hydrocortisone for slower absorption from the gastrointestinal (Gl) tract. The extremely water-soluble 21-sodium succinate and 21-sodium phosphate esters are used for IV or IM injection in the management of emergency conditions that can be treated with anti-inflammatory steroids. The phosphate ester is completely ... 

Substitution on l-t-butyl-3,4-dimethylphosphole by 2-carboethoxy caused a net upheld shift of — 6.8 ppm, and the same effect was observed for 2-acetyl (A — 7.6 ppm). The upheld shift may be more a consequence of steric influences from the bulky t-butyl group, and not indicative of a conjugative effect. Other ester derivatives are known ((25) and (26)) but are not useful in ascertaining conjugative effects without related model compounds. 

As with the ethyl ester, other ester derivatives can be alkylated through their lithium enolates.Use of the menthyl ester provides a route to chiral silanes (eq 8). ... 

Given that the highly reactive acetate-derived silyl ketene acetal 24 displayed a broad substrate scope with respect to the aldehyde, we decided to explore other ester-derived silyl ketene acetals. Again, our hope was that these more reactive nucleophiles would maintain broad reactivity with respect to the aldehyde. The diastereoselectivity of this catalyst system could also be investigated, in this case by employing propanoate-derived silyl ketene acetals. The catalyst had already shown a high level of control over the facial approach of the nucleophile to the activated... 

Acidify the residue in the flask with dUute sulphuric acid and distil off 10-15 ml. of the solution. Test a smaU portion of the distillate for acidity, and also observe the odour. Neutralise the main portion with sodium hydroxide solution (add a drop of phenolphthalein to act as indicator), evaporate to smaU bulk, and convert the sodium salt into the p-bromophenacyl ester or into some other suitable derivative (Section 111,85) determine the m.p. of the derivative. 

Acid derivatives are made directly from acids or by conversion from other acid derivatives depending on their stabihty. The most important are esters (RCOiEt), amides (RCO2NR2), anhydrides (RCOO COR) and add clilorides (RCOCI). Arrange these in an order of stabilily, the most reactive at the top of the list, the most stable at the bottom. 

Acrolein, acrylamide, hydroxyalkyl acrylates, and other functional derivatives can be more hazardous from a health standpoint than acryhc acid and its simple alkyl esters. Furthermore, some derivatives, such as the alkyl 2-chloroacrylates, are powerful vesicants and can cause serious eye injuries. Thus, although the hazards of acryhc acid and the normal alkyl acrylates are moderate and they can be handled safely with ordinary care to industrial hygiene, this should not be assumed to be the case for compounds with chemically different functional groups (see Industrial hygiene Plant safety Toxicology). 

The organotin maleate and maleate half-ester derivatives also exhibit this bleaching effect reportedly by a Diels-Alder addition reaction (18). The reaction is specific to the organotin maleates other organotin carboxylates containing normal dieneopltiles fail to produce similar results (19). 

Alkyl boric acid esters derived from straight-chain alcohols and aryl boric acid esters are stable to relatively high temperatures. Methyl borate is stable to 470°C (11). Trialkoxyboranes from branched-chain alcohols are much less stable, and boranes from tertiary alcohols can even decompose at 100°C (12). Decomposition of branched-chain esters leads to mixtures of olefins, alcohols, and other derivatives. 

The p-phenylbenzoate ester was prepared to protect the hydroxyl group of a prostaglandin intermediate by reaction with the benzoyl chloride (Pyr, 25°, 1 h, 97% yield). It was a more ciystalline, more readily separated derivative than 15 other esters that were investigated. It can be cleaved with K2CO3 in MeOH in the presence of a lactone. ... 

Other methods for the preparation of cyclohexanecarboxaldehyde include the catalytic hydrogenation of 3-cyclohexene-1-carboxaldehyde, available from the Diels-Alder reaction of butadiene and acrolein, the reduction of cyclohexanecarbonyl chloride by lithium tri-tcrt-butoxy-aluminum hydride,the reduction of iV,A -dimethylcyclohexane-carboxamide with lithium diethoxyaluminum hydride, and the oxidation of the methane-sulfonate of cyclohexylmethanol with dimethyl sulfoxide. The hydrolysis, with simultaneous decarboxylation and rearrangement, of glycidic esters derived from cyclohexanone gives cyclohexanecarboxaldehyde. 

In aqueous dioxane, the endo-anti isomer gave a product mixture consistent of alcohol N and the corresponding ester (derived from capture of the leaving group p-nitrobenzoate). The other isomers gave much more complex product mixtures which were not completely characterized. Explain the trend in rates and discuss the structural reason for the stereochemical course of the reaction in the case of the endo-anti isomer. 

Ehminations of HX to give double bonds offer considerable scope for selectivity and choice of reaction conditions. The dehydration of alcohols is the most common example of this class and may be achieved directly or through intermediate derivatives. In most cases, such derivatives are transient species formed in situ, but sometimes e.g. sulfonates, certain other esters and halides) they are isolated and characterized. Eliminations from jS-substituted ketones are very facile. The dehydration of jS-hydroxy ketones has been covered in section V. 

Ortho esters are one of the few derivatives that can be prepared from acids and esters that protect the carbonyl against nucleophilic attack by hydroxide or other strong nucleophiles such as Grignard reagents. In general, ortho esters are difficult to prepare directly from acids and are therefore more often prepared from the nitrile. Simple ortho esters derived from normal alcohols are the least stable in terms of acid stability and stability toward Grignard reagents, but as the ortho ester becomes more constrained, its stability increases. 

We recently synthesized cationic polymers containing imidazole (e g. 68 (SZ811) and 69 (SZ11—3—3)] by reacting poly [N-(2,4-dinitrophenyl)-4-vinyl-pyridinium chloride] with histamine or histamine mixed with other amino derivatives ll8 The hydrolyses of neutral and anionic esters with the models followed saturation kinetics in alkaline media. 

Tertiary alkyl azides can be prepared by stirring tertiary alkyl chlorides with NaN3 and ZnCl2 in 82 ° or by treating tertiary alcohols with NaN3 and CF3-COOH or with HN3 andTiCl4 or BF3. Acyl azides, which can be used in the Curtius reaction (18-14), can be similarly prepared from acyl halides, anhydrides, " esters, or other acyl derivatives. ° Acyl azides can also be prepared... 

The above scheme satisfies much of the metabolic data however, some of it is speculative, and it is certainly incomplete. The evidence for the formation of the a-hydroxylated intermediate is circumstantial. The acetate ester of a-hydroxylated dimethylnitrosamine has been prepared (12.13) and has been found to be a potent, directly acting carcinogen (14). Other esters of a variety of a-hydroxylated nitros-amines have also been prepared (15). While it has been shown that DMN acetate is hydrolyzed to hydroxymethylmethyl-nitrosamine by an esterase enzyme, it has been pointed out that these derivatives of the a-hydroxylated nitrosamines also dissociate to N-nitrosoimmonium ions (15 16). 

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