Acetyl protection with

In these cydizations, the reaction can be terminated in other ways than elimination of /3-hydrogen. Typically the reaction ends by an anion capture process[154]. The following anion transfer agents are known H, OAc , CN, S02Ph, CH(C02R)2, NHRj, CO/ROH, and RM [M = Sn(IV), B(lll), Zn(II)]. Trapping with an amine after alkene insertion to give 189 and 190 is an example. A-Acetyl protection is important in this reaction[155]. 

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Fluorination of trifluoromethanesulfonyl carbohydrates with cesium fluoride under forcing conditions (130 °C in dimethylformamide) [55] or the use of acetyl protected substrates [56] gives considerably lower yields... 

In synthesis of the alkaloid tjipanazole E (19b), the required symmetric dichloro-indolo[2,3-fl]carbazole 20a was obtained in a two-step procedure starting fi-om 4-chlorophenylhydrazine hydrochloride and 1,2-cyclohexanedione employing a Fischer indolization. Subsequent attachment of an acetyl-protected glucopyranosyl moiety to one of the nitrogens, followed by cleavage of the protective groups with ammonia in methanol, produced the desired natural product (91X7739). 

The living character of the ROMP promoted by the initiator Ru(CHPh)(Cl)2 (PCy3)2 (Cy = cyclohexane) was tested with the synthesis of diblock, triblock, and tetrablock copolymers of norbornene derivatives carrying acetyl-protected glucose, [2,3,4,6-tetra-O-acetyl-glucos-l-O-yl 5-norbornene-2-carboxylate], A or maltose groups, [2,3,6,2/,3/,4/,6/-hepta-0-acetyl-maltos-1-O-yl 5-norbornene-2-carboxylate], B, shown in Scheme 41 [102]. The AB, ABA, and ABAB structures were prepared by sequential addition of monomers with narrow molecular weight distributions to quantitative conversions. 

SAMSA-fluorescein, 5- [2(and 3)-5-(acetylmercapto)-succinoyl]amino fluorescein, is a fluorescent probe containing a protected sulfhydryl group. In its protected state, the compound is unre-active. The acetyl-protecting group can be removed by treatment with dilute NaOH at pH 10.0 (Figure 9.9). The resulting free sulfhydryl derivative can be used to label thiol-reactive crosslinkers or to couple with sulfhydryl residues on proteins and other molecules. After activating... 

The concept of using diazaquinones for diene system protection was accomplished in the case of some vitamin D derivatives, as shown in Scheme 37 (86JOC4819). Acetyl vitamin D2152 was protected with phtha-lazinedione 83a, providing a mixture of both possible stereoisomeric adducts from which 153 was isolated. Then usual ozonolysis procedure afforded aldehyde 154, which after the Wittig coupling and hydrogenation provided 155. The most difficult part of the sequence proved to be the deprotection of this compound, but this transformation was accomplished... 

Wong and coworkers showed that 5-azido sialyl donors protected with O-acetyl ester are useful for a-selective glycosylations of primary hydroxyls (Scheme 4.6e) [169]. It was proposed that the linear and electron-withdrawing nature of the C-5 azido moiety stabilizes the reactive axial acetonitrile adduct to allow the incoming nucleophile to approach the a-face in an SN2-like fashion. In addition, a chemose-lective glycosylation method has been developed for the synthesis of NeuAca-(2 —> 9) NeuAc as thioglycoside donor for use in the subsequent glycosylations [169]. 

Of note, a very recent report shows that SIRTl (sirtuin class of HDAC), that was shown to participate in axonal protection (Araki et al, 2004), could be acting in a neuroprotective way in ALS (Fischer et al, 2005). As noted earlier, this class of HDAC is insensitive to classical HDAC inhibitors, but it should be kept in mind reinstating acetylation homeostasis with classical HDACi might indirectly biased sirtuin s regulations as well. 

The resolution was then based on the enzymatic propanolysis of this derivative in dioxane as solvent. Lip Novozyme 435 selectively cleaves the L-form of the oxazolone producing an L-enriched (81-87% ee) 2-acetamido-3-(heteroaryl)propionic acid propyl ester, the dynamic aspect of the process being based on the continual racemization of the residual oxazolone. The propyl group was then removed with alkali and a second selective enzymatic step to remove the acetyl protecting group with Fluka Acylase 1 produced the L-amino acid at better than 99% ee (Scheme 13). 

It proved most difficult to synthesize the glycoside derivatives where one of the hydroxyl groups in the 3- or 4-position was protected with an acetyl group whereas tte 2- d 6-position were blocked with benzyl groups. The methyl 4-6>-acetyl-2,6-di- - enzy galactoside 18 could however be relative easily obtained in 70% total yield via a one-pot reaction (Scheme 6). ... 

However, by protecting the -NHg group by acetylation reaction with acetic anhydride, the nitration reaction can be controlled and the p-nltro derivative can be obtained as the major product. 

It has also been suggested to reduce the nitro group to an amino group, protect it with an acetyl protection, oxidize the sulfur atom to a sulfone using potassium dichromate, and then remove the protective acetyl group by hydrolysis [48-50]. 

Several methods were described for the selective de-S-acetylation of 0-acetyl protected 1-thioglycoses. Sodium methoxide in methanol at low temperature (below -20 °C) was known to afford mainly the de-S-acetylated compound [16] or exclusively this compound when the reaction was quenched at low temperature by adding H-l- resin [17]. Demercuration of tetra-O-acetyl-l-phenylmercury(II)-thio- -D-glucopyranose (12) (Scheme 4) obtained by treatment of (8e) with phenylmercury(II)acetate afforded a convenient synthesis of tetra-0-acetyl-l-thio-/3-D-glucose (8a) [18]. This sequence applied to the a-anomer (10a) (Scheme 3) led to the expected de-S-acetylated compound (10b) [19]. Chemoselective deprotection of thioacetate at the anomeric position of peracetylated 1-thioglycoses was also achieved in good yield by action of cysteamine in acetonitrile or hydrazinium acetate in DMF [20,11]. 

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