Neuartige Porphyrinoide für Chemie und Medizin durch biomimetische Synthesen

Abstract

Telefax: Int. + 2151188-7703 rechtfertigt, sie als Porphyrinoide zu bezeichnen, da sie alle aus einer gemeinsamen Biosynthesevorstufe, dem Uroporphyrinogen I11 3, hervorgehen (Schema l)L5-']. CO, H CO, H 1 2 Porphyrin Porphyrinogen COaH 3 Uroporphyrinogen 111 Schema 1. Strnktur der Porphyrinoide 1-3. Fur die Bedurfnisse der Organismen entwickelte die Natur eine Bioproduktion von Porphyrinoiden, deren Dimensionen abgeschatzt werden konnen. Beginnen wir mit dem Porphyrinoid Vitamin B,, , dessen Mange1 perniciose Anamie verursacht. Der Mensch benotigt nur die auI3erordentlich geringe Menge von taglich 0.001 mg Vitamin BIZ; das ergibt fur die gesamte Erdbevolkerung einen Jahresbedarf von etwa 2000 kg. Der zur

Figure Eights, Möbius Bands, and More: Conformation and Aromaticity of Porphyrinoids

“…ilies of porphyrin analogues, such as calixpyrroles, [27,28] calixphyrins, [29] Schiff-base macrocycles, [12,30] and vinylogous porphyrins [30,31] will fall outside the scope of this Review. The relationship between conformation and aromaticity is particularly consequential in expanded porphyrins, which will be our primary area of interest.…”

“…Inversion of meso carbons is also observed and it becomes a nearly standard feature of vinylogous porphyrins, containing meso bridges of three or more carbons. [31] As a consequence of inversion, the polygon defined by ring centroids and meso bridges is no longer convex. Obviously, ring inversion will not lead to a reduction of curvature if the subunit possesses rotational symmetry (and hence t subunit = 0), as it is the case of p-phenylene.…”

“…The "annulene in porphyrin" concept, dating back to the 1960s, [94] was exploited with remarkable success in the research on porphyrin isomers [95] and vinylogous porphyrins. [31] In the annulene model of porphyrinoid aromaticity, a conjugation pathway (CP) is searched within the p system that meets the following conditions: 1) it passes through all subunits, that is, it encompasses the macrocycle; 2) it can be filled with an alternating sequence of formal single and double bonds, that is, it can be represented by two KekulØ structures; 3) it does not involve charge separation (see Scheme 1 for representative examples). When these conditions are met, the length of the CP, denoted N, is equal to the number of p electrons in the CP and corresponds with the observed aromatic or antiaromatic character of the macrocycle, in accordance with the Hückel rules.…”

“…This feature, which is in line with theoretical predictions, is convincingly demonstrated by the series vinylogous porphyrins containing up to 34 electrons in their CPs. [31] The strength of a ring current is often expressed in terms of Dd, the chemical shift difference between the most deshielded and most shielded protons. Distortions from planarity, which occur in the majority of systems discussed in this Review, generally result in diminished Dd values, as a consequence of the less efficient p orbital overlap in torsionally deformed structures.…”

“…[31] As shown in Scheme 2, the full name of a porphyrinoid will include several of the following: 1) substituent list; 2) designation of replaced heteroatoms or cyclic subunits; 3) length of the conjugation pathway [N] (Section 3.1); 4) systematic name indicating the number of cyclic subunits; 5) designation of the meso pattern. The latter designator, which is of the general form (a.b.c.d…), shows how many carbon atoms separate consecutive pairs of adjacent cyclic subunits.…”