Isobacteriochlorins structure

Isay reaction, 2, 79-80 3, 259 Ismelin 7, 656 Isoalloxazine oxidation states, 1, 252 Isoaminopterin synthesis, 3, 327 Isoarsindolines, 1, 543-544 Isoarsinoline, tetrahydro-synthesis, 1, 552-553 stability, 1, 552 Isoascorbic acid structure, 4, 552 ( )-IsoavenacioIide synthesis, 1, 416 Isoazapenem synthesis, 1, 465 Isobacteriochlorin synthesis, 4, 419 Isobacteriochlorin, dimethyl-biosynthesis, 1, 105 Isobacteriochlorin, methyl-biosynthesis, 1, 105 Isobacteriochlorin, trimethyl-biosynthesis, 1, 105 Isobarbituric acid Mannich reaction, 3, 71 synthesis, 3, 133... 

The important biological role of the isobacteriochlorins has decisively influenced the development of synthetic approaches leading to the isobacteriochlorin class of compounds. All of the naturally occurring isobacteriochlorins contain geminally dialkylated structural parts in the saturated pyrrole rings, which require special approaches for their synthesis. Until the discovery of siroheme and sirohydrochlorin, this structural element could only be found in vitamin B,2. Using the synthetic potential, which was invented during numerous syntheses of... 

The modification of porphyrins leading to isobacteriochlorins by C —C-bond formation is important to obtain a wide range of structurally different isobacteriochlorins which can then be further transformed. Protoporphyrin, deutoroporphyrin and hematoporphyrin (readily accessible from red blood pigment) are interesting and useful starting materials in the synthesis of isobacteriochlorins. 

We examine here possible structural effects that may result from or accompany the generation of the primary photoproducts, and speculate about the consequences of concomitant changes in distances,conformations, relative orientations and charges on the electronic profiles of and interactions between the BChls, BPheos and their radicals. Because the primary events in green plant photosynthesis also involve a series of chlorophyll donors and acceptors ( ), similar trends should therefore prevail for chlorophyll radicals as well. Furthermore, radicals of porphyrins and hydroporphyrins (saturated porphyrins such as chlorins and isobacteriochlorins) have been... 

We present first crystallographic results for porphyrins, chlor-ins and isobacteriochlorins that illustrate the wide range of structural variations that can be assumed by the porphyrin skeleton ... 

The examples cited above represent part of an increasing body of structural information on chlorophylls, chlorins, bacteriochlorins and isobacteriochlorins (10-14 and references therein) that points to the remarkable flexibility of these molecules This ability of the macrocycle to adjust is not limited to hydroporphyrins but is also observed in porphyrins 5,10,15,20-tetra-n-propylporphinato lead (II) assumes a "roof" shape by folding along an axis defined by two opposite methine carbons with the two planes of the "roof" inclined at 22 to one another (15) In contrast, triclinic 5,10,15, 20-tetraphenylporphinato cobalt (II) is distinctly saddle shaped with the 3 carbons of adjacent pyrrole rings lying 40 66 and -0 66A above and below the plane of the four nitrogens (16) ... 

Near IR spectra—See Electronic absorption spectra New IR spectra, R sphaeroides reaction centers, 207,208f NH-tautomer structure, porphyrins with nonsymmetrical substitutions, 84 NH-tautomerism, porphyrins with nonsymmetrical substitution, 74-93,89-91 Ni(II)-reconstituted hemoglobin—See Nickel-reconstituted heme proteins Nickel isobacteriochlorin... 

The structure of factor III, the trimethyl isobacteriochlorin, is worthy of note. Preliminary studies had suggested the structure (81), which was in better accord with a subsequent ring contraction to the corrinoid skeleton involving oxidation at C-20 followed by extrusion of formaldehyde. However, the 13C NMR spectrum of factor III (as its octamethyl ester) enriched biosynthetically with [13CH3]methionine and [5-13C]ALA (Scheme 25) shows both the meso and meso- methyl carbons as doublets, a feature in accord with substitution of... 

Figure 16-6 Structures of isobacteriochlorin prosthetic groups. (A) Siroheme from nitrite and sulfite reductases (B) acrylochlorin heme from dissimilatory nitrite reductases of Pseudomonas and Paracoccus.

A crystal structure of the complex [ZnL(py)] (L= isobacteriochlorin) has been reported the metal is in a distorted planar environment.11 ... 

Iron(III) complexes, tetraphenylporphyrinatobenzene-thiolatobenzenethiol-, 517 Iron(IV) complexes phosphines SHAB theory, 1040 Iron cupferronate structure, 510 Iron methoxide physical properties, 346 Iron pivalate basic, 303 Iron proteins iron-sulfur group, 773 Isobacteriochlorins, 851 Isobutyric acid, hydroxy-metal complexes IR spectra, 470 Isobutyric acid, 2-hydroxy-metal complexes NMR, 467 Isocitric acid... 

Several macrocyclic ligands are shown in Figure 2. The porphyrin and corrin ring systems are well known, the latter for the cobalt-containing vitamin Bi2 coenzymes. Of more recent interest are the hydroporphyrins. Siroheme (an isobacteriochlorin) is the prosthetic group of the sulfite and nitrite reductases which catalyze the six-electron reductions of sulfite and nitrite to H2S and NH3 respectively. The demetallated form of siroheme, sirohydrochlorin, is an intermediate in the biosynthesis of vitamin Bi2, and so links the porphyrin and corrin macrocycles. Factor 430 is a tetrahydroporphyrin, and as its nickel complex is the prosthetic group of methyl coenzyme M reductase. F430 shows structural similarities to both siroheme and corrin. 

The isobacteriochlorin 8 serves as an example. Two protons distributed between the four nitrogen atoms with a 50% occupancy at each site were found experimentally. It has been suggested that two tautomeric forms (8a, b) contribute, equally to the solid-state structure. Two Ca—N bonds (A = 0.051 A) and two C —Cm bonds (A = 0.077 A) are significantly different as a result of the superposition of the tautomeric forms (82JA2376). 

The general structures of iron porphyrins are shown in Figure 1, together with the stractures of closely related ring systems, including iron chlorins and isobacteriochlorins, thiaporphyrins, tetraazaporphyrins, phthalocyanines, corroles, and texaphyrin. Examples of substituents present on commonly investigated natural and synthetic iron porphyrins are also included. 

The sequence of the various steps between uroporphyrinogen III and cobyrinic acid has been the subject of much recent work. A major advance in this area was the observation that sirohydrochlorin (77), the iron-free prosthetic group of the enzyme siroheme, could be modified to accommodate its role as a biosynthetic intermediate. Subsequently a dimethyl isobacteriochlorin (factor II) isolated from P. shermanii was shown to be identical with sirohydrochlorin from E. coli sulphite reductase. The complete stereostructure of (77) was elucidated by a series of biosynthetic experiments using [4- C]- and [5- C]-ALA and independently by more classical structural arguments (B-79MI10401, B-79MI10402>. Sirohydrochlorin labelled biosynthetically from [4- C]ALA and [ CHsJmethionine is incorporated into cobyrinic acid by cell-free extracts of F. shermanii without loss or migration of label. 

The three foregoing intermediates 53,12 and 55 are all readily oxidised to the corresponding aromatic chlorins or isobacteriochlorins when handled in air. Thus, 53 affords Factor 154,12 gives sirohydrochlorin 56 and 55 is converted into Factor III 57. In fact, most of the research leading to the structures of these three precorrins was carried out on the stable dehydrogenated products [ 1,28,77,78]. Fortunately, the aromatic systems 56 and 57 could be reduced either enzymical-ly or by catalytic hydrogenation to return to precorrin-2 12 and precorrin-3A 55, respectively [1,28,77,78]. It should also be noted that sirohydrochlorin 56 is the metal-free macrocycle corresponding to sirohaem 7 [6-8], Scheme 1. 

Fig. 4. Ring structures of (a) Porphyrin (b) Chlorin (c) Bacterioch-lorin and (d) Isobacteriochlorin.

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