A Synthetic Approach to the Isobacteriochlorin Macrocycle

Montforts, Franz‐Peter; Ofner, Silvio; Rasetti, Vittorio; Eschenmoser, Albert; Woggon, Wolf‐D.; Jones, Keith; Battersby, Alan R.

doi:10.1002/anie.197906751

Cited by 39 publications

(20 citation statements)

References 18 publications

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“…Such phenomena have been studied in [21][22][23]. It was found that for a structurally related compound with no cyano group (2,2,7,7,12,13,17,18-octamethylisobacteriochlorin (H 2 OMiBC), synthesized in [24]), no such dynamic equilibrium is observed when it is exposed to light. A characteristic feature of H 2 OMiBC in n-octane at 77 K is the irreversibility of the conversion of centers c → a; and when the solution is thawed, the concentration of the pigment remains unchanged, i.e., the centers do not degrade.…”

Section: (Ii)mentioning

confidence: 98%

Electronic structure and spectra of NH-isomers of isobacteriochlorin

2006

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ev UDC 539.19Using the restricted and unrestricted Hartree-Fock method (RHF and UHF) with the AM1 Hamiltonian, we have calculated the geometric structure of the NH-isomers of isobacteriochlorin and its meso-cyano derivative. We have used the CNDO/S method for all the considered structures to calculate the transitions to excited electronic states. We have analyzed the effect of taking into account electron correlation on the results of the calculations of the chemical and geometric structure and the electronic spectra. For the a isomer with the imino hydrogens opposite each other, we obtained a planar structure corresponding to literature x-ray diffraction data. For the aromatic c isomer and other isomers with the imino hydrogens adjacent to each other, the calculations lead to a substantial nonplanarity of the macrocycle (defined mainly by the tilt of the pyrrole rings) and also deviation of the NH bond from the plane of the pyrrole ring. The ground-state energies of the a and c isomers have close values, which generally explains the observed NH tautomerism. We calculated the dipole moments of the isomers in the ground state and the excited state. The results of the calculation of the characteristics of the excited states with UHF geometry on the whole seem to be preferred over those with RHF geometry. We show that only for the aromatic c isomer can we describe the electronic absorption spectrum within a four-orbital model.

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Section: (Ii)mentioning

confidence: 98%

Electronic structure and spectra of NH-isomers of isobacteriochlorin

2006

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“…Isobacteriochlorins (iBCs), porphyrins in which two adjacent pyrrole rings are reduced, have recently elicited (1)(2)(3)(4)(5)(6)(7)(8)(9) considerable interest because the prosthetic groups of sulfite and nitrite reductases contain siroheme (10), an iron-iBC that has eight carboxylic acid side chains (Fig. la).…”

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confidence: 99%

π cation radicals of ferrous and free base isobacteriochlorins: Models for siroheme and sirohydrochlorin

Chang

Hanson

Richardson

et al. 1981

Proc. Natl. Acad. Sci. U.S.A.

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Theoretical and experimental optical, redox, and paramagnetic results are presented for models of siroheme, the iron isobacteriochlorin prosthetic group of nitrite and sulfite reductases, and of sirohydrochlorin, the metal-free siroheme that is an intermediate in the biosynthetic pathway to vitamin B12. The facile oxidation of many isobacteriochlorins, which distinguishes them from porphyrins and chlorins, suggests that the siroheme macrocycle itself may undergo oxidation in the multi-electron enzymatic cycles that reduce nitrite to ammonia and sulfite to hydrogen sulfide. Extended Huckel MO calculations (i) help rationalize the redox properties of isobacteriochlorins compared with those of porphyrins and chlorins; (ii) indicate that Fe(IH) pyridine carbonyl [(py) (CO)] complexes ofisobacteriochlorins, unlike those of porphyrins and chlorins, should undergo oxidation from the macrocycle rather than the metal to yield i1 cation radicals; (iii) suggest that, in hexacoordinated Fe(II) isobacteriochlorin complexes, the site of oxidation-i.e., the metal or the macrocyclewill depend on the ligand field induced by the axial ligands; and (iv) predict similar unpaired spin density profiles for metal-free and (py) (CO)Fe(H) isobacteriochlorin radicals. Experimental data for three isomeric free-base and (py) (CO)Fe(II) complexes of dimethyloctaethylisobacteriochlorins support the theoretical calculations and establish the existence of Fe(II) isobacteriochlorin 17 cations in vitro.Isobacteriochlorins (iBCs), porphyrins in which two adjacent pyrrole rings are reduced, have recently elicited (1-9) considerable interest because the prosthetic groups of sulfite and nitrite reductases contain siroheme (10), an iron-iBC that has eight carboxylic acid side chains (Fig. la). The enzymes catalyze (10) the six-electron reductions ofsulfite to hydrogen sulfide and nitrite to ammonia. In green plants, the latter reaction, N02 + 8H+ + 6e --NH4+ + 2H20, is light driven with photosynthetically reduced pyridine dinucleotide serving as electron donor to the active enzyme (11):Chlorophyll -+ NADPH -+ flavoprotein --ferredoxin -+ nitrite reductase.An additional biological role has been attributed (12, 13) to iBCs with the realization that sirohydrochlorins, demetallated sirohemes, are intermediates in the biosynthetic pathway ofthe corrin, vitamin B12.A salient feature of the iBC skeleton is its ease of oxidation and difficulty of reduction compared with those of porphyrins and chlorins (1)(2)(3)8). This facile oxidation has led us to propose (1-6) that the siroheme macrocycle itself may undergo redox reactions in the multi-electron enzymatic reductions ofthe substrates to ammonia and hydrogen sulfide, and we have pre- (See Fig. 4

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“…Unter dem Templat-Einfluss des Zink-Ions liess sich der lineare tetrapyrrolische Metallkomplex rac-8a,b mit DBU (1,.0]undec-7-en) zum (Hexamethylsulfolenochlorinato)zink 9 cyclisieren. Wie in früheren Arbeiten gezeigt [3b] [13] [16], wird der Ringschluss durch Dehydrocyanidierung und Ausbildung einer exocyclischen Enamin-Doppelbindung an C(20) eingeleitet und durch nucleophilen Angriff des Enamins an der Bromoimino-Struktur der Position 4 abgeschlossen. Bisherige Arbeiten zur Chlorin-Bildung [13] durch baseninduzierte Cyclisierung hatten gezeigt, dass DBU in Sulfolan oder KO t Bu in t BuOH geeignete Bedingungen darstellen, um aus den entsprechenden Bilinen in guten Ausbeuten Chlorine zu erhalten.…”

unclassified

“…und extrahierte erschöpfend mit CH 2 Cl 2 . Nach Filtration über Watte und Eindampfen chromatographierte man an Alox (CH 2 Cl 2 /AcOEt 19 : 1): 12,6 mg (66,7%) rac- 1,13,1,15,1,20,1,25,1,31 (6s,je 3 H,2 MeÀC(19), MeÀC(20)); 2,02,2,04,2,06,2,08,2,10,2,14,2,16,2,17 (8s,je 3 H,MeÀC(8), MeÀC(9), MeÀC (13), MeÀC (14)); 2,58, 2,97 (AB, 2 J AB 15,87, 2 H, HÀC(18) (rac8a)); 2,70, 2,90 (AB, 2 J AB 16,95,2 H,HÀC(18) (rac-8b)); 4,11,4,12,4,34,4,39 (4s,je 2 H,HÀC(1), HÀC(3)); 5,31,5,35,5,96,6,01,6,49,6,…”

unclassified

“…IR (KBr): 3300w (NH), 2960w (CH), 2910w (CH), 2850w, 2220w (CN), 1700s (CO), 1610s, 1590s, 1580s, 1520m, 1460w, 1440w, 1420w, 1350m, 1300w, 1250m, 1220s, 1190w, 1140w, 1130m, 1110m, 1090m, 1060m, 800w, 780w. 1 H-NMR (270 MHz, CDCl 3 ): 0,78, 0,93, 1,18 (3s, 2 MeÀC(18), MeÀC (19)); 1,12 (X von ABX 3 , 3 J AX 8, CO 2 CH 2 Me); 2,00, 2,03,2,07,2,15,2,16,2,28 (6s,18 H,MeÀC(2), MeÀC (3), MeÀC (7), MeÀC(8), MeÀC(12), MeÀC(13)); 2,42, 2,72 (AB, 2 J AB 17,4, 2 HÀC (17)); 4,05, 4,15 (AB von ABX 3 , 2 J AB 12, CO 2 CH 2 Me); 5,30, 5,74, 6,58 (3s, HÀC(5), HÀC(10), HÀC (15) H 7,51, N 13,22; gef. : C 72,60, H 7,52, N 13,26. Daten von rac-12a,b: DC (Alox; CH 2 Cl 2 /AcOEt 10 : 1): R f 0,9 (rac-12a), 0,8 (rac-12b).…”

mentioning

confidence: 99%

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Synthese von Sulfolenobilinen und deren Cyclisierung zu Chlorinatozink-Fulleren-Dyaden

Kutzki

Walter

Montforts

2000

HCA

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Prof. Dr. Albert Eschenmoser zu seinem 75. Geburtstag gewidmet Synthesis of Sulfolenobilins and Their Cyclization Directed to Chlorinatozinc-Fullerene DyadsA novel chlorinatozinc-fullerene dyad 18 was synthesized to model the photosynthetic reaction center. The synthetic key step for the formation of the dyad 18 is an unusual one-pot reaction of the (sulfolenobilinato)-nickel rac-16a,b with concomitant generation of the chlorin macrocycle and linkage to the [5,6]fullerene-C 60 -I h . This one-pot reaction is a complex cascade of single reaction steps with a total yield of 32% and an average yield of 83% for the individual steps. The chlorinatozinc-fullerene dyad is so far one of three examples that contain chlorin moieties, the chromophores in naturally occurring photosynthetic systems.

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A Synthetic Approach to the Isobacteriochlorin Macrocycle

Cited by 39 publications

References 18 publications

Electronic structure and spectra of NH-isomers of isobacteriochlorin

Electronic structure and spectra of NH-isomers of isobacteriochlorin

π cation radicals of ferrous and free base isobacteriochlorins: Models for siroheme and sirohydrochlorin

Synthese von Sulfolenobilinen und deren Cyclisierung zu Chlorinatozink-Fulleren-Dyaden

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