Tripyrrole

Cation (14) leads straightforwardly to tripyrrole, by way of protonated pyrrole dimer (18), the structure of which corresponds with the structures proved for 2-methyl- and 2-phenyl-pyrrole dimers. 

The trimer having been produced, protonation of the central pyrrolidine nitrogen occurs, and the formal positive charge then sufficiently retards further electrophilic attack on the two pyrrole nuclei to allow the isolation of tripyrrole. 

The synthesis of porphyrins from monopyrrolic, dipyrrolic, tripyrrolic and tctrapyrrolic precursors requires, even for an experienced porphyrin chemist, a substantial amount of time and effort to accomplish. As an alternative to these total synthetic routes, nature provides a source of prefabricated porphyrins. Among the several porphyrins which can be isolated from natural material,s the red blood pigment heme, protoporphyrin dimethyl ester81 b and hemato-porphyrin, both derived from heme, are the only compounds which can be obtained in sufficient amounts. Heme is available in almost unlimited amounts from slaughter-house waste. From 1 L of blood ca. 1 g of heme can be isolated.81 b Currently, heme is offered commercially by chemical retailers at a relatively low price so that is cheaper to buy hemin than to perform a self-isolation in the laboratory. 

A synthesis of the immunosuppressive agent undecylprodigiosine involved a Suzuki coupling between 57 and triflate 62 to give tripyrrole 63 [57]. The corresponding Stille reaction was unsuccessful... 

Condensation of 5,5 -diunsubstituted dipyrrylmethanes (210) with one mole of a 2-formyl-5-methylpyrrole (211) affords high yields of tripyrroles (212), apparently uncontaminated with by-products due to reaction of the pyrrole at both ends of (210). The tripyrrole intermediates can then be reacted with a different formylpyrrole (213) to give the appropriate a,c-biladiene (214) cyclization then gives good yields of porphyrins (215) (Scheme 15) (73DOK(210)1090>. 

In the Rh (entry 37) or Pd thiaporphyrin derivatives (entry 47), the thia-pyrrole-tripyrrole macrocycle is not planar. Because the thiaporphyrin only carries one central proton, anions are required as axial ligands in its chelates to neutralize the latter. Pd(SDPDTP) (entry 47) does not have an anion. It has been formed by one-electron reduction from Pd(SDPDTP)Cl. An extra electron... 

Bruice, T. C., Mei, H.-Y., He, G.-X., Lopez, V. Rational Design of Substituted Tripyrrole Peptides That Complex with DNA by Both Selective Minor-Groove Binding and Electrostatic Interaction with the Phosphate Backbone. Proc. Natl. Acad. Sci. USA. 1992, 89, 1700-1704. 

An intramolecular reaction, which could be viewed as an electrophilic attack on nitrogen, is mentioned under the reactions of the carbocyclic ring (see Section 7.21.6.1.3) <83CPB1518>. The dihydrobenzodipyrrole (45) was acylated on the pyrrolidine nitrogen atom (87CC1406). The oxidation of some benzodipyrroles, e.g. compound (6), and related tripyrroles, to their JV-oxides can be viewed as an electrophilic attack on nitrogen. 

Various [c c] fused benzo-, di-, and tripyrroles are formed by the reaction of poly(halomethyl) benzenes with amines. The dihydrocompounds formed were further dehydrogenated to fully conjugated derivatives <88ZN(B)125>. 4,6-Diacetylresorcinols reacted with hydrazine in 2-methoxy-ethanol to form [1,2-c 5,4-c ]benzodipyrazoles <88JMC2034>. 

Although more practical than the 4 + 1 approach, the 3 + 2 route was also found early on to be limited by difficulties associated with obtaining the requisite tripyrrolic ( 3 ) and bipyrrolic ( 2 ) precursors. Thus, even though the initial reports of Woodward and Johnson served to pique the curiosity of the porphyrin community, the chemistry of sapphyrins remained undeveloped until 1991, when Sessler and coworkers introduced an improved synthesis of sapphyrins. This new synthesis is based on simple high-yielding routes to both dicarboxyl-substituted... 

Streptomyces showdoensis incorporates 95% 1-[ C] or 2-[ C]acetate into showdomycin (1) in the maleimide ring only [22], and this confirms earlier C findings. The exclusive incorporation of l-[ C]acetate at C-1, and 2-[ C]acetate at C-2, C-3 and C-4 can be explained with reference to the Krebs cycle and the malic enzyme. C Spectra on 0.1 M solutions of labelled showdomycin in 13 mm tubes required 6 hr accumulation time. Furthermore, C-labelled alanine, proline, glycine and serine have been fed to the bacterium Serratia marcescens [23] to trace the origin of the carbon atoms in its tripyrrole metabolite, prodigiosin (2). The methoxy group is probably derived from methionine whereas the C-2 methyl is from alanine. 

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