Acetyl-substituted

In the linear konjac mannan, the degree of acetylation profoundly affects the solubility and flow properties of this hydrocolloid. The acetyl substitution prevents self-association of the mannan chains, but following deacetylation chain interactions become more energetically favorable [230]. 

The benzoyl groups are all axial, and are oriented with their planes approximately normal to the mean plane of the pyranose ring. The bond lengths are normal. The C-5-0-5, O-5-C-l, C-l-O-1, O-l-C(Bz) bond-lengths are 142.0,138.4,143.5,136.0 pm, which are characteristic of 1-O-benzoyl or 1-O-acetyl substitution. 

Acetyl-substituted Proposed Dicationic Products Yields... 

G. K. Hamer No, it is not. Using the educated eye (once you know its there in the A type) if you look at the B type very closely you see a tiny peak in the same position. If you look at the 220 MHz proton spectrum it is much more obvious. There is a very small amount in the bovine. The main differences between the two sources are a) N-acetyl substitution for N-sulfate and b) the change in uronic acid. 

A -acylaziridines substituted with an electron-withdrawing group produce a 2,4-disubstituted oxazoline as the major product. Borontrifluoride etherate (BF3 OEt2) has also been used successfully for an Al-benzoyl, but not an N-acetyl-substituted aziridine (Scheme 8.58). ... 

Kato, T. and Morita, Y., C-glycosylflavones with acetyl substitution from Rumex acetosa L., Chem. Pharm. Bull, 38, 2277, 1990. 

Liu, K.C.S. et al., Flavonol glycosides with acetyl substitution from Kalanchoe gracilis. Phytochemistry, 28, 2813, 1989. 

Chen, Z., Schols, H. A., Voragen, A. J. G. (2004). Differently sized granules from acetylated potato and sweet potato starches differ in the acetyl substitution pattern of their amylose populations. Carbohydr. Polym., 56, 219-226. 

Under mild conditions nitration and acetylation of hexahelicene give the 5-nitro-and 5-acetyl substitution product as the main product in about 50% yield. In both cases another monosubstitution product is formed, which was identified tentatively by NMR as the corresponding 8-substituted hexahelicene. From the relative rates of detritiation (krel) or the partial rate factors (f) given in Table 27, it seems more probable, however, that the 7-isomers are formed as the side product, as the positional reactivity order of detritiation is C(5) >C(7) >C(8) >C(1) >C-(4) >C(6) >C(2) > C-(3). The preferred reactivity at C(5), found in electrophilic substitutions, is predicted by all the simple Hiickel parameters, whereas the next two positions are correctly predicted by Nr and Lr. Judging from Nr-, Fr- and Lr-values the C-(l) position does not experience much steric hindrance in the H-exchange. Relative to some other positions (C(4), C(6)) its reactivity is higher than expected. The Mulliken overlap population predicts, however, the highest reactivity for C(l) and leaves room for the supposition that this position is considerably masked. 

The acetyl-substituted complexes, initially prepared by Jager36 by direct synthesis, have served as the basis for all of the work in this area. It has been shown that the acetyl group can be replaced by substitution, especially nitration, where reaction conditions are rather vigorous.39 The acetyl-substituted complexes are not only nucleophilic at carbon, a property exhibited in the above reaction, but they are also nucleophilic at oxygen, being vinylogous amides, and undergo... 

In polar solvents such as chloroform, dichloromethane, acetone, and acetonitrile, the fluorescence quantum yields of 97a-d decrease by varying degrees (see Table 19). Moreover, in the case of the phenyl and acetyl derivatives 97c and 97d, the rather drastic decrease of the structured fluorescence from the locally excited anthracene is associated with the appearance of a structureless, red-shifted emission which is attributable to an intramolecular exciplex. For 97d, in which the electron acceptor properties of the aromatic carbonyl moiety are enhanced by p-acetyl substitution, exciplex emission is dominant even in toluene solution (see Figure 22). 

Diprotonated, superelectrophilic intermediates were suggested to be involved in both conversions. Considering protonated aldehydes, benzal-dehyde gives a carboxonium ion that is significantly resonance stabilized and thus unreactive towards aromatic substrates such as o-dichlorobenzene or nitrobenzene. Pyridinecarboxaldehydes, however, show much higher electrophilic reactivities due to their ability to form via TV-protonation the superelectrophile (5, eq 8).10 A similar situation is seen in the hydroxyalkylation reactions of acetyl-substituted arenes. Acetophenone is fully protonated in excess triflic acid, but the resulting carboxonium ion (6) is... 

This is reasonably close to the experimentally determined value of AFF = 11.1 kcal/mol for the superelectrophilic cyclization of 62 (eq 12). Another computational study showed that the energy barriers dramatically decrease for the electrocyclization when the monocations are protonated to form superelectrophiles. In the case of 63, cyclization provides the acetyl-substituted fluorene in 70% yield from CF3SO3H (Scheme 5). At the B3LYP/6-31 level of theory, dication 64 is estimated to have a cyclization barrier to fluorene of 8.5 kcal/mol, compared to a value of 25 kcal/mol for the cyclization of monocation 65. 

The structure of 1-acetyl-substituted [838] and 1-thiono-substituted 6-nitroben-zotriazoles [824, 839, 840] used as acylation and thioacylation agents, respectively, in the peptide synthesis has been confirmed by H and 13C NMR spectra. 

A-Nitro and acetyl-substituted 1,3,5,7-tetrazocanes are important compounds as explosives and propellants <1996CHEG-II(9)705>. In the syntheses of the nitro-substituted 1,3,5,7-tetrazocanes, their processing, and application, it is possible that they come into contact with ammonium nitrate, or they are directly mixed with this oxidant. Thermal reactivity of the nitro-substituted 1,3,5,7-tetrazocanes has been examined by means of nonisothermal differential thermal analysis <2005MI11>. It has been established that impurities of ammonium nitrate can destabilize some A-substituted 1,3,5,7-tetrazocanes and that this effect is due to acidolytic attack of nitric acid. 

The ultraviolet spectra of phenoxazine and of several 2-substituted phenoxazines, recorded in Table I, exhibit two bands at 224-247 m/i (log e 4.30-4.73) and 318-328 mfi (log e 3.84-4.01), while the acetyl-substituted phenoxazines present a third absorption band at about 270 m(i (aromatic ketone band). It can be seen from this table that A-alkylation has only a slight influence upon the position and intensity of these bands, and merely produces small bathochromic shifts. 

Icmt catalyzes the methyl esterification of the prenylated cysteine residue after Reel has proteolyzed the -CaaX-containing proteins. The first step in identification of the minimal substrate for Icmt was through identification of AFC (Figure 9.2) as described above. Interestingly, farnesylcys-teine (FC), which is devoid of the acetyl substitution, was not a substrate but did possess some activity as an inhibitor [51], suggesting that the free amine of FC requires modification for catalytic turnover. Alterations in the stereochemistry about the FC backbone also appeared to be detrimental to substrate activity. The stereoisomer, d-AFC, was not a substrate for Icmt but was a modest mixed-type inhibitor of the enzyme. AFC-methyl ester (AFC-Me) was also reported to be a mixed-type inhibitor with respect to both l-AFC and -adenosylmethionine (SAM), the methyl donor, with Ki values of 41 and 73 pM, respectively [52,53] The farnesyl homocysteine homolog of AFC is not a substrate for the enzyme however, the racemic DL-homocysteine farnesyl derivative is in fact a weak inhibitor [40]. Similar to the results with racemic prenylcysteine, these data demonstrate that the linker between the carboxylate and thioether moieties is critical for substrate activity. 

Trichothecenes can be divided into two groups based on their site of action on protein synthesis. Trichothecenes with hydroxyl and acetyl substitutions at both C-3 and C-4, such as T-2 toxin, DAS, verrucarin A, preferentially inhibit initiation while DON, trichodermin, crotocin, and verucarol inhibit elongation and/or termination (McLaughlin et al, 1977). Trichothecenes inhibit both DNA and RNA synthesis... 

The effect of N-acetyl substitution in methionine on the nature of transients formed after one-electron oxidation was studied as a function of pH and NAM concentration. The observed absorption bands with X = 290 nm, 360 nm, and 490 nm were respectively assigned to a-(alkylthio)alkyl, hydroxysulfuranyl and dimeric radical cations with intermolecular three-electron bond between sulfur atoms. N-acetylmethionine amide (NAMA) (Chart 7) represents a simple chemical model for the methionine residue incorporated in a peptide. Pulse radiolysis studies coupled to time-resolved UV-Vis spectroscopy and conductivity detection of N-acetyl methionine amide delivered the first experimental evidence that a sulfur radical cation can associate with the oxygen of an amide function vide infra). ... 

The bifuran-containing corrole 2.39 was also subject to acylating conditions. In this instance, treatment of corrole 2.39 with acetyl chloride using aluminum trichloride as the Lewis acid afforded the C(5)-acetyl-substituted corrole derivative 2.245 in 31% yield (Scheme 2.1.89). In addition to this product, a di-substituted corrole was also obtained. This was presumed to be either a 2,18- or a 3,17-diacetyl-substituted corrole. However, no evidence was put forward in support of either of these assignments. 

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