Acid-mediated hydrolysis

The absorption efficiency of the different carotenoids is variable. For example, (3-cryptoxanthin has been reported to have higher absorption efficiency than a-cryptoxanthin in rats (Breithaupt and others 2007). Carotenoids must be liberated from the food before they can be absorbed by intestinal cells (Faulks and Southon 2005). Mechanical disruption of the food by mastication, ingestion, and mixing leads to carotenoid liberation (Guyton and Hall 2001). The enzymatic and acid-mediated hydrolysis of carbohydrates, lipids, and proteins (chemical breaking of the food) also contributes to carotenoids liberation from the food matrix (Faulks and Southon 2005). Once released, carotenoids must be dissolved in oil droplets, which are emulsified with the aqueous components of the chyme. When these oil droplets are mixed with bile in the small intestine, their size is reduced, facilitating the hydrolytic processing of lipids by the pancreatic enzymes (Pasquier and others 1996 Furr and Clark 1997 ... 

The nitroalcohol precursor was resolved by the lipase-catalyzed acylation of the hydroxy group. The nitrobutyraldehyde was obtained by acid-mediated hydrolysis of the nitrodiethylacetal and used directly in the aldolization reaction after pH adjustment to 7.5. 

The Clauson-Kaas reaction between 2,5-dimethoxytetrahydrofuran 19 and phenylsulfonamide performed in the presence of triflic acid (TfOH) led to either pyrrole 20, indole 21, or carbazole 22 depending on the amount of triflic acid used <07TL4047>. The latter two compounds were formed by the annulation of pyrrole or indole by butanedial (generated by the acid-mediated hydrolysis of 19). A double Clauson-Kaas sequence starting with hydrazine allowed for the preparation of 1,1 -bipyrrole <07JOC93 95>. 

The preparation of ester 13 is performed by an acid-mediated hydrolysis of nitrile 12 in methanol. The conditions used are quite vigorous concentrated sulfuric acid, reflux (65 °C), overnight. However, in this reaction the addition of methanol to the protonated nitrile gives the corresponding acetimidic acid methyl ester, and subsequent hydrolysis of this intermediate provides the desired ester 13 in 90 % yield. 

Reduction of the carbamate-protecting group by the action of LiAlH4 afforded 742b in 92% yield. An acid-mediated hydrolysis of the silyl ether provided ( + ) -dehydrocuscohygrine (743) in 89% yield. Further oxidation of the alcohol under Jones conditions produced the desired target 744 in 73% yield. 

Pd(OH)2/C in the presence of HC1 and cyclohexene provided 45 in 64% yield. This reaction is believed to proceed via intermediate oxime 44, which undergoes acid-mediated hydrolysis and ketalization to afford the product.25 Use of other reducing agents, such as TiCb/NH40Ac/H20, or hydrogenation with Pd/C and H2 provided lower yields of the desired compound. The spiroketal 45 is a substructure of the y-rubromycin family of natural products, which have shown activity against HIV reverse transcriptase and DNA helicase. 

While corn yield per acre has a steadily increasing trajectory, there is a long-term interest in the use of hgnocellulosic biomass for the production of fuel ethanol. Acid-mediated depolymerization of saw dust (and other materials) into sugar was noted in 1819 by Braconnot [15, 16]. This acid-mediated hydrolysis and subsequent fermentation came to be known as the Classen process [17, 18], and by 1910 there were reports of economically successful production of ethanol from wood waste [19, 20]. But interest in these processes waned and they were largely forgotten, as evidenced by the fact that the 2013 opening of a facility... 

Ichiyanagi, T., Oikawa, K., Tateyama, C., Konishi, K., Acid mediated hydrolysis of blueberry anthocyanins, Chem. Pharm. Bull., 2001, 49, 114-117. 

Morimoto reported the synthesis of omaezakianol through propose that acid-mediated hydrolysis occurs at the dimethyl... 

Acid-mediated hydrolysis of 5-halopyrrole-2-carboxylates provides access to 5-carboxy-3-pyrrolin-2-ones, but this transformation often lacks the regioselectivity of other methods. This reaction was first reported by Siedel (1943LAC144). In a more recent example, Battersby and coworkers have treated 5-bromopyrrole-2-carboxylate 548 with sulfuric add in methanol, and a mixture of 3-pyrrolin-2-ones 549 and 550 was obtained in low yield (Scheme 156 1988PT(1)1557). These reaction conditions led to both hydrolysis of the bromine and deprotection of the <-butyl ester followed by decarboxylation. In a related reaction involving a symmetrical substrate, Lugtenberg and de Groot converted 5-bromo-2-trichloroacetyl-3,4-dime-thylpyrrole into 3,4-dimethyl-3-pyrrolin-2-one via treatment with NaOH (1982MI2). 

The MAO-N D5 variant was also employed in the desymmetrization of N-xmprotected mcso-pyrrolidines yielding the corresponding A -p3orolines these compoxmds are useful intermediate respective templates for the synthesis of highly substituted proline analogues through a frans-selective nucleophilic addition of designated nucleophiles like cyanide, followed by an acid-mediated hydrolysis (Scheme 2.38) [140]. 

Tertiary amines may be cleaved by ethyl chloroformate in certain circumstances. A-Demethylation has been noted. For example, tropine acetate (eq 14) is readily converted to nortropine hydrochloride on refluxing with ethyl chloroformate and subsequent acid-mediated hydrolysis of the intermediate urethane. 

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