Acetyl resistance

Cellulose Triacetate. Cellulose acetate having 92% or more of the hydroxyl groups acetylated is referred to as triacetate. This fiber is characteristically more resistant to alkaU than the usual acetate and may be scoured, generally, in openwidth, with aqueous solutions of a synthetic surfactant and soda ash. 

The properties of chlorine azide resemble those of bromine azide. Pon-sold has taken advantage of the stronger carbon-chlorine bond, i.e., the resistance to elimination, in the chloro azide adducts and thus synthesized several steroidal aziridines. 5a-Chloro-6 -azidocholestan-3 -ol (101) can be converted into 5, 6 -iminocholestan-3l -ol (102) in almost quantitative yield with lithium aluminum hydride. It is noteworthy that this aziridine cannot be synthesized by the more general mesyloxyazide route. Addition of chlorine azide to testosterone followed by acetylation gives both a cis- and a trans-2iddMct from which 4/S-chloro-17/S-hydroxy-5a-azidoandrostan-3-one acetate (104) is obtained by fractional crystallization. In this case, sodium borohydride is used for the stereoselective reduction of the 3-ketone... 

Acylation of 7-ACA with 2-thienylacetylchloride gives the amide cephalothin (43). Displacement of the allylic acetyl group by pyridine affords the corresponding pyridinium salt cephalori-dine (44). Both these compounds constitute useful injectable antibiotics with some activity against bacteria resistant to penicillin by reason of penicillinase production. 

Surprisingly, acetylation in hot pyridine yields the pyridinium salt 10. The amino group has amidine character and is resistant to diazotization, and condenses only with reactive aldehydes such as formaldehyde and trichloroacetaldehyde.41... 

Amino-5-hydrazinopyrazole dihydrochloride 300 is a good source for the synthesis of this type of heterocyclic compound [78JCS(P1)885] and it was prepared by reaction of malononitrile with two equivalents of hydrazine. Reaction of 300 with ethyl pyruvate afforded 301. Unstable hydra-zone 302 formed when 300 was boiled with diacetyl rapidly cyclized to 303. Reaction of 300 with benzil gave 304 directly, which gave an acetyl derivative and resisted reductive deamination. On the other hand, a polymer was isolated from the reaction of 300 with glyoxal (Scheme 65). 

The major mechanism of resistance to chloramphenicol is mediated by the chloramphenicol acetyltransferases (CAT enzymes) which transfer one or two acetyl groups to one molecule of chloramphenicol. While the CAT enzymes share a common mechanism, different molecular classes can be discriminated. The corresponding genes are frequently located on integron-like structures and are widely distributed among Gramnegative and - positive bacteria. 

It has been shown that an AAC enzyme variant (AAC (6 )-Ib-cr, cr for ciprofloxacin resistance) found in various Enterobacteriaceae is capable of A-acetylating fluoroquinolones with an unmodified piperazinyl substituent at the amino nitrogen. Although the increase in MIC is low, this plasmid encoded quinolone resistance determinant can augment further development of clinically relevant resistance. 

At3g06550 - are deficient in wall-bound acetate. It would be interesting to test their resistance, lignin depositions and other physiological parameters under the influence of pathogens. It may be that these experiments will make clear the role of polysaccharide acetylation. 

Fig. 9.2 Modification of AGACs (e.g. kanamycin and amikacin) by resistance enzymes. A, acetylation (AAC) B, adenylylation (AAD) C, phosphorylation (APFl).

Some agonists, such as methacholine, carbachol and bethanecol are structurally very similar to ACh (Fig. 6.6). They are all more resistant to attack by cholinesterase than ACh and so longer acting, especially the non-acetylated carbamyl derivatives carbachol and bethanecol. Carbachol retains both nicotinic and muscarinic effects but the presence of a methyl (CH3) group on the p carbon of choline, as in methacholine and bethanecol, restricts activity to muscarinic receptors. Being charged lipophobic compounds they do not enter the CNS but produce powerful peripheral parasympathetic effects which are occasionally used clinically, i.e. to stimulate the gut or bladder. 

Stohl EA, SE Brady, J Clarty, J Handelsman (1999) ZmaR, a novel and widespread antibiotic resistance that acetylates zwittermicin A. J Bacteriol 181 5455-5460. 

In Hg-resistant bacteria that are resistant to organic forms of Hg such as phenylmercuric acetate and methylmercury chloride, lyases are involved in the fission of the C-Hg to form Hg + and benzene or methane, and the enzyme has been partly purified (Schottel 1978). The Hg + may then be reduced to nontoxic Hg°. The situation under anaerobic conditions for sulfate-reducing bacteria is complicated by the possibility of both methylation and demethylation in the same strain (Pak and Bartha 1998), plausibly by operation of the acetyl-CoA pathway (Choi et al. 1994 Ekstrom et al. 2003). Under anaerobic conditions, demethylation, though not methylation, has been reported for a methanogen (Pak and Bartha 1998). 

Acetyl bromide cleaves dibenzyl sulfide, while diethyl or diisopropyl are resistant (27). 

The scope of the deamination reaction was extended to the characterization of heparin segments containing 2-acetamido-2-deoxy-D-glucosyl residues by removing (by hydrazinolysis) the N-acetyl groups and cleaving with nitrous acid (at pH 4) the otherwise resistant segments.113,232... 

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