N-Acetyl derivatives

AcOCgFs, Et3N, DMF, 80°, 12-60 h, 72-95% yield. This reagent reacts with amines (25°, no Et3N) selectively in the presence of alcohols to form N-acetyl derivatives in 80-90% yield. 

Purification as their N-acetyl derivatives is satisfactory for primary, and to a limited extent secondary, amines. The base is refluxed with slightly more than one equivalent of acetic anhydride for half to one hour, cooled and poured into ice-cold water. The insoluble derivative is filtered off, dried, and recrystallised from water, ethanol, aqueous ethanol or benzene (CAUTION toxic ). The derivative can be hydrolysed to the parent amine by refluxing with 70% sulfuric acid for a half to one hour. The solution is cooled, poured onto ice, and made alkaline. The amine is steam distilled or extracted as above. Alkaline hydrolysis is very slow. 

The structures of these two isomers of mono-N-acetyl derivative of 4 were decided on the basis of their NMR spectra as discussed in the part of structural studies. 

N-Acetylation of Kasugamycinic Acid (9a). A solution of kasugamycinic acid (225 mg.) dissolved in 10 ml. of water was treated with acetic anhydride (0.3 ml.) under cooling sodium bicarbonate was used to keep the pH 7.2 and stirring continued for 30 minutes. The reaction product was passed through Dowex 50W-X2 (H form) and the column was washed with water. The combined filtrate was subjected to lyophilization to afford 234 mg. of a crude N-acetyl derivative. Its infrared spectrum showed strong absorptions at 1740 cm-1 characteristic of oxamic acid group. The N-acetyl derivative (178 mg.) was treated with 40 ml. 

The N-acetyl derivatives of 2-aminohexoses give a reaction even in the absence of acetylacetone [4]. 

Aminoglycoside antibiotics la 107,270, 284,354,380,423,434 Amino groups lb 194 4-Aminohexoses, N-acetyl derivatives lb 233... 

Figure 13-10. Glucosamine (2-amino-D-glucopyra-nose) a form). Galactosamine is 2-amino-D-galactopy-ranose. Both glucosamine and galactosamine occur as N-acetyl derivatives in more complex carbohydrates, eg, glycoproteins.

Selectivity studies with DTU indicated marked discrimination in the clathrate formation 23,45). As in other types of clathrates, the steric factor is important in differentiation between compounds of similar functionality but different shape. For example, DTU forms crystalline complexes with some alcohols (methanol, ethanol, propanol, 1-butanol) but not with others (2-butanol). It complexes the ethyl esters of N-acetyl derivatives of glycine, alanine, methionine and aspartic acid, but not of proline, serine, phenylalanine and glutamic acid. 

Commercial neomycin is a complex mixture of aminoglycoside antibiotics originally isolated from a culture of Stn.tptomyc.zi, ( n.adiaz by Waksman and his co-workers in 1949. The principle components of the mixture are neomycin B(I) and neomycin C(II) together with a small quantity of neaminel, a degradation product of neomycin formerly known as neomycin A. Table 1 shows the content variability of neomycin B and C and neamine in commercial samples of neomycin as reported in the literature. Neomycins LP-A, LP-B and LP-C which chemically are the mono N-acetyl derivatives of neomycins A, B and C may also be present in small amounts. Several other minor components have recently been identified as paromamine, paromomycin I and paromomycin II. (Also known as neomycins D, E and F respectively). 

To determine the relative amounts of neomycins B, C and neamine by a radio chemical method, Kaiser 2 separated the -labelled N-acetyl derivatives by paper chromatography and quantitated the chromatograms by liquid scintillation counting. A coefficient of variation of 3.6% was obtained. 

In orange dyes of the haloheterocyclic type, the reactive system is invariably attached via the nitrogen of the ] acid coupler. In vinylsulphone dyes, on the other hand, it is normally more convenient to use as diazo component an intermediate such as 7.38 or 7.39 bearing the precursor grouping together with an N-acetylated derivative of ] acid or y acid as coupler, structure 7.93 being typical. 

According to Trautman (16), PNA was converted almost exclusively to p-nitrophenol in the mouse with 24 hours, nearly all of which was excreted in the urine as glucuronide, sulfate, glucoside, and unextractable products the mouse tissue retained only about 1% of the original dose. By comparison, the sea urchin metabolized PNA slowly p-nitrophenol and its conjugates accounted for only about 6% of the metabolites and most of the remainder (90%) was p-anisidine (p-methoxyaniline) and its N-acetyl derivative. 

Acetylation Primary amines Hydrazines Acetyltransferases (Acetylcoenzyme A) N-acetylated derivatives... 

Phenyl esters of anthranylic acid give upon irradiation ortho-mano-benzophenones, and their N-acetyl derivatives 264 give ortfto-Af-acetamido-benzophenones 265, which can be converted into quinolones (266) with basic treatment (Scheme 67) [188]. 

Reduction of oximino esters, i.e. oximes of keto esters, is very useful for the preparation of amino esters. Reductions are very selective since the oximes are easily reduced by catalytic hydrogenation over 10% palladium on carbon in ethanol (yield 78-82%) I094, by aluminum amalgam in ether (yields 52-87%) [750, 70P5], or by zinc dust in acetic acid (yield 77-78%). None of these reagents attacks the ester group. The last mentioned reaction gives an N-acetyl derivative [1096. ... 

Scheme 6 (1991JHC379)). Interestingly, N-acetyl derivative 35b affords N-unsubstituted compound 36b in 62% yield. 

Nucleophilic substitution can occur at an sp -hybridized carbon in dihydrooxazines. 3-Methoxydihydrobenzoxazine 154 was treated with trimethylsilyl cyanide with boron trifluoride catalysis (Equation 7) to give the 3-cyanohenzox-azine 155 <1986H(24)3483>, and the N-acetylated derivative of 154 reacted similarly <1983JHC45>. 

Hydrogen peroxide and A -bromosuccinimide cause oxidative degradation-dimerization of dihydrooxazine 145 and its N-acetylated derivative 146 to give 190 <1982AP761>. 

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