Pyrrole 1,2-diamino- from

Returning to the synthesis of 2,3-few(benzimidazol-2-yl)quinoxalines 100a-g (Scheme 6.41 Table 6.5) it should be noted that in one case, i.e., in the case of the synthesis of 2,3-fcw(benzimidazol-2-yl)-6-nitroquinoxaline lOOe, the less-reactive l,2-diamino-4-nitrobenzene 5h was used as a reagent. In this case a derivative of pyrrolo[l,2-a]quinoxaline containing one benzimidazolone (in position 1) and two benzimidazole (at positions 2 and 3) fragments in the newly formed pyrrole ring from the reaction mixture were isolated in trace amounts as an unexpected product. The formation of compound 159 could be due to the condensation of 3-(benzimidazo-2-yl) quinoxalin-2(lf/)-one 37s with its predecessor-3-(benzimidazol-2-yl)methylene-... 

In the reaction of ethyl cyanoacetate with sulphur and base, 2,4-diamino-3,S-di(ethoxycarbonyl)thiophen was only the minor product (20%). The major products were pyrrole derivatives. From cyanoacetamide and benzyl cyanide no thiophen derivatives were obtained. The reaction of (9a) with (10) in the presence of triethylamine yields the aminothiophen (11), while (9b) gives the hydroxy thiophen (12). If the salt of ethyl (thiobenzoyl)... 

In connection with the synthesis of cytohalasin B, a pyrrole derivative 13 was prepared from methyl (5)-3-aminophenylbutyrate (78JA7775). In connection with the synthesis of l,2,4-triazolo[4,3-a]pyrazine derivatives with human Renin inhibitor activity, a /3,y-diamino acid derivative was transformed into a pyrrolidin-2-one (91JMC151). 

The Fe " " complex of the linear hexadentate A, A, 5 ,iS ,A, A -coordinating ligand derived from l,8-diamino-3,6-dithiaoctane and pyrrole-2-aldehyde has been synthesized and characterized, especially by Mossbauer spectroscopy.The hexadentate tripodal NsSs-donor triazamacrocyclic ligands (196) and (197) give brown-violet and green black Fe complexes, respectively the former is predominantly high-spin, the latter predominantly low-spin. In the complex of (1 the Fe—N bond distances are between 2.06 A and 2.08 A, Fe—S between 2.269(3) A and 2.288(3) A. ... 

Potts and McKeough81 have recently obtained several interesting mesoionic azapentalenes 83, 84 by reaction of the appropriate 1,4-dicarbonyl compound with phosphorus pentasulfide. Compounds 83 and 84 can be written as dipolar structures, but participation of sulfur d-orbitals allows nonpolar forms to be envisaged. MO calculations neglecting rf-orbital participation predict the thieno[3,4-c]pyrrole system (84) to be very unstable.430 A related system 86 has been prepared by Japanese workers63 from the diamino-r-triazole (85) and sulfur dichloride. 

The enzyme catalyzing the condensation of two molecules of 5-AL to one of PBG (Fig. 11) is widely distributed in animal tissues (72-75), and the use of 5-AL in porphyrin biosynthesis has been shown in spinach (74), yeast (74), and bacteria (59, 74, 76). The preparation from ox liver (74) and that from rabbit reticulocytes (75) have been considerably purified and show very similar characteristics. The enzyme from ox liver is rather specific for its substrate. 2,5-Diamino-4-ketopentanoic acid, 6-amino-5-ketohexanoic acid, and aminoacetone form no pyrrole with this enzyme, and are only weakly inhibitory if at all. The rabbit enzyme does not act on amino acetone, nor does it seem to form a mixed pyrrole in the presence of both 5-AL and aminoacetone. The kinetics of this enzyme are of interest since it is a rare case of an enzyme catalyzing a reaction between two identical. substrate molecules. Both the rabbit and ox liver enzymes follow simple Michaelis kinetics over the range 10 to 2 X M substrate concentration. The simplest interpretation of these data, together with some related chemical evidence (75), is that the enzyme binds both molecules of substrate specifically, the first more tightly than the second. In this respect it resembles most the enzyme-coenzyme substrate reactions. The reaction... 

---