Sulfanilamide acetylation

The metabolism of a number of sulfonamides, such as sulfanilamide. sulfamethoxazole (Gantanol). sulfisoxa-zx>le (Gantrisin). sulfapyridine (major metabolite from azo reduction of sulfasalazine. Azulfidine), and sulfamethazine. " " occurs mainly by acetylation at the N-4 position. With sulfanilamide, acetylation also takes place at the sul-... 

Govier, W.C. (1965) Reticuloendothelial cells as the site of sulfanilamide acetylation in the rabbit. Journal of Pharmacology and Experimental Therapeutics, 150, 305-308. 

White powder. Characteristic thiol odor- May be dried in vacuo over phosphorus pentoxide at 34°. uv max 259.5 nm (e 16,800), Fairly strong acid. pK 9.6 (thiol) pK 6,4 (secondary phosphate) pK 4,0 (adenine NH3+). Soluble in water. Practically insol in ethenol, ether, acetone. Strength of solns expressed in Lipmann units (that amount of Co A which gives half-saturation of the sulfanilamide acetylation system). One unit of Co A weighs 2,43 y and contains 0,7 y pantothenic acid 1.0 mg CoA equals 413 Lipmann units. The pure dry coenzyme is bast stored in evacuated ampuls at room temp. Readily oxidized by air to the catalytically inactive disulfide. 

Guseva, A.R. and M.G. Borikhina Sulfanilamide acetylation as a means of coenzyme assay in higher plants Biokhimia 23 (1958) 272-276. 

In a few cases, A/ -heterocycHc sulfanilamides have been prepared by the condensation of an active heterocycHc haHde with the sulfonamide nitrogen of sulfanilamide or its A/-acetyl derivative in the presence of an acid-binding agent. Sulfapyridine, sulfadiazine, and sulfapyrazine have been made by this method (1), but the most important appHcation is probably for the synthesis of sulfachlorapyridazine (9) and sulfamethoxypyridazine (10) (45). 

In another approach to the required functionality, the sodium salt of acetyl sulfanilamide (196) is condensed with butyl... 

Another observation on oxalate formation is that other a-keto acids, such as oxalosuccinic acid (74) and a-ketoglutaric acid (106) do not seem to yield oxalate directly but indirectly (123). This appears to be due to the fact that only oxaloacetic acid can function as an acetate donor. In this connection the intervention of Coenzyme A may be considered, since it is reported to function in the acetylation of sulfanilamide and choline (73) and recently was shown to take part in the enzymatic synthesis of citric acid. This concept may be illustrated as follows ... 

Two of these systems were studied as models—the acetylation of choline in brain to give acetyl choline (Hebb, Nachmansohn), and of sulfanilamide (the active component in prontosil, Chapter 3) in liver (Lipmann). Sulfanilamide is rapidly inactivated by acetylation on the p-amino group and then excreted. Sulfanilamide is easily diazotized the diazonium salt formed can be coupled with N-( 1 -naphthyl)ethylenedi-amine dihydrochloride to give a pink derivative (Bratton and Marshall, 1939). This formed the basis for an elegant colorimetric assay. Only the free p-amino group reacts, so that as acetylation proceeded color formation diminished. 

Sulfisoxazole Sulfisoxazole, ATi-(3,4-dimethyl-5-isoxazolyl)sulfanilamide (33.1.19), is synthesized by reacting 4-acetylaminobenzenesulfonyl chloride with 5-amino-3, 4-dimethylisoxazol (33.1.17), which is in turn synthesized by heterocyclization of 2-methy-lacetylacetonitrile with hydroxylamine, and subsequent acidic hydrolysis (hydrochloric add) of the protective acetyl group in the resulting product (33.1.18) [18,19]. 

Although the two forms of the enzyme have preferred substrates, there is overlap between them such that no substrate seems to be exclusively acetylated by one or the other. Some preferred NAT1 substrates are p-aminobenzoic acid and p-aminosalicylic acid and sulfanilamide, whereas preferred substrates for NAT2 include isoniazid, hydralazine, procainamide, and dapsone. 

The acetylation of sulfanilamide is illustrated in Figure 4.68, and it can be seen that either the N4 amino nitrogen or the N1 sulfonamido nitrogen can be acetylated, or indeed both. 

Figure 4.68 Acetylation of sulfanilamide on the N1-sulfonamido or N4-amino nitrogen to give the N1- and N4-acetyl and N1, N4-diacetyl derivatives.

Acetylation. Most mammalian species are able to acetylate aromatic amino compounds, the major exception being the dog. Thus, for a number of amino compounds such as procainamide (chap. 4, Fig. 43), sulfadimethoxine, sulfamethomidine, sulfasomizole, and the N4 amino group of sulfanilamide (chap. 4, Fig. 68), the dog does not excrete the acetylated product. However, the dog does have a high level of deacetylase in the liver and also seems to have an acetyltransferase inhibitor in the liver and kidney. Consequently, acetylation may not be absent in the dog, but rather the products may be hydrolyzed or the reaction effectively inhibited. 

The dog does, however, acetylate the Nl, sulfonamido group of sulfanilamide (chap. 4, Fig. 68), and also acetylates aliphatic amino groups. The guinea pig is unable to acetylate aliphatic amino groups such as that in cysteine. Consequently, it excretes cysteine rather than N-acetylcysteine conjugates or mercapturic acids. Birds, some amphibia, and insects are also able to acetylate aromatic amines, but reptiles do not use this reaction. 

Lipmann wondered what nature used in their place. His approach in seeking the biological "active acetate" is one that has been used successfully in solving many biochemical problems. He first set up a test system to examine the ability of extracts prepared from fresh liver tissue to catalyze the acetylation of sulfanilamide (Eq. 14-2). A specific color test was available for quantitative determination of very small amounts of the... 

SGLT1-Na+ dependent 417 Sulfanilamide 473s, 720s acetylation of 720 Sulfatase(s) 526 Sulfate esters... 

This reaction sequence is similar to the sequence used to synthesize sulfanilamide. Key steps are (1) treatment of aniline with acetic anhydride to modulate reactivity, (2) reaction of acetanilide with chlorosulfonic acid, (3) treatment of the chlorosulfonate with the heterocyclic base, and (4) removal of the acetyl group. 

For the logarithmic value of kAc, Equation 13 and its modification, Equation 14, were formulated, where KA° is the dissociation constant of sulfanilamide, a, p c p, and c are constants, and [H+] is the hydrogen ion concentration in the blood. We used Equation 14 to analyze the acetylation data. The second term on the left of Equation 14 expresses the dissociation effect of the free drug, but it does not mean that the neutral form is only responsible for metabolism. 

Why is an acetyl group added to aniline (making acetanilide) and then removed to regenerate the amine group in sulfanilamide ... 

---