Seco (tetrapyrrole)
The prefix seco in tetrapyrrole nomenclature[1] signifies that the macrocyclic ring of a porphyrin, chlorophyll, or corrin is opened at the specified position to the corresponding acyclic (linear) tetrapyrrole.[2] This nomenclature reflects chemical reactions involving respective ring openings and ring closures.
Seco-tetrapyrroles as products of biological and chemical degradation
Linear tetrapyrroles originating from natural chlorophyll breakdown during plant senescence, known only since the 1990s, were first named as 4,5-seco-phytoporphyrins, since about 2014 as phyllobilins, with this systematic name expressing their origin from chlorophyll and their structural relation to bile pigments (fig. 1).[3][4]
Chemical ring cleavage of cyclic tetrapyrroles also produces seco-derivatives, as in the photooxygenolysis of vitamin B12 (fig. 2).[5][6]
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Seco-corrins in corrin syntheses
In the Harvard (Woodward)/ETH (Eschenmoser) variant of the two total syntheses of vitamin B12,[7][8] the corrin macrocyle is built by coupling an A/D- (Harvard) and a B/C (ETH) component, first at meso-C-15 between rings D and C, followed by ring closure of the resulting seco-corrin at C-5, using the Eschenmoser sulfide contraction developed at ETH for both coupling reactions (fig. 3).[9][10]
Figure 3. Corrins from seco-corrins via A/B ring closure by Eschenmoser sulfide contraction:[9] important step in the Harvard/ETH variant of the total syntheses of vitamin B12
Figure 4. Corrin from A/D-seco-corrin via photochemical A/D ring closure:[11][12] key step in the ETH variant of the total syntheses of vitamin B12
In the photochemical ETH variant of these total syntheses, the corrin ring is closed directly between rings A and D – as typical for corrins, meso position C20 missing – in an A/D-seco-corrin → corrin cycloisomerization (fig. 4).[13][12]
Other corrins were synthesized by Eschenmoser et al. from seco-corrins by A/B ring closure via imidoester–enamine C–C condensation,[14] sulfide contraction,[10] or by photochemical A/D cyclization.[15]
References
- ↑ Moss, Gerard P. (1988). "Nomenclature of tetrapyrroles: Recommendations 1986". European Journal of Biochemistry. 178 (2): 277–328. doi:10.1111/j.1432-1033.1988.tb14453.x. ISSN 0014-2956.
- 1 2 "TP-6 and TP-7 Linear Tetrapyrroles". Nomenclature of Tetrapyrroles. Retrieved January 31, 2026.
- ↑ Kräutler, Bernhard (2014). "Phyllobilins – the Abundant Tetrapyrrolic Catabolites of the Green Plant Pigment Chlorophyll". Chemical Society Reviews. 43 (17): 6227–6238. doi:10.1039/C4CS00079J. ISSN 1460-4744.
- 1 2 Kräutler, Bernhard (2016). "Breakdown of Chlorophyll in Higher Plants—Phyllobilins as Abundant, Yet Hardly Visible Signs of Ripening, Senescence, and Cell Death". Angewandte Chemie, International Edition. 55 (16): 4882–4907. doi:10.1002/anie.201508928. ISSN 1433-7851. PMC 4950323. PMID 26919572.
- 1 2 Kräutler, Bernhard; Stepánek, René (1985). "Photooxygenolysis of Vitamin B12". Angewandte Chemie, International Edition in English. 24 (1): 62–64. doi:10.1002/anie.198500621. ISSN 0570-0833.
- 1 2 Kräutler, Bernhard; Stepanek, Rene (1991). "Photooxygenolysis of vitamin B12 and related corrins: cobalt(III)corrins as substrates and quenchers for singlet oxygen (1Δg)". Photochemistry and Photobiology. 54 (4): 585–592. doi:10.1111/j.1751-1097.1991.tb02060.x. ISSN 0031-8655.
- ↑ Woodward, R. B. (1973). "The total synthesis of vitamin B12". Pure and Applied Chemistry. 33 (1): 145–178. doi:10.1351/pac197333010145. PMID 4684454.
- ↑ Eschenmoser, Albert (2025). "3.5. The corrin saga and the synthesis of vitamin B12 (1960–1972)". Prizes are Good but Discoveries are Better. Lives in Chemistry – Lebenswerke in der Chemie. Berlin: GNT-Verlag GmbH. pp. 112–163. ISBN 978-3-86225-136-0.
- 1 2 Roth, M.; Dubs, P.; Götschi, E.; Eschenmoser, Albert (1971). "Sulfidkontraktion via alkylative Kupplung: Eine Methode zur Darstellung von β‐Dicarbonylderivaten. Über synthetische Methoden, 1. Mitteilung". Helvetica Chimica Acta (in German). 54 (2): 710–734. doi:10.1002/hlca.19710540229. ISSN 0018-019X.
- 1 2 Blaser, Hans-Ulrich; Winnacker, Ernst-Ludwig; Fischli, Albert; Hardegger, Bruno; Bormann, Dieter; Hashimoto, Naoto; Schossig, Jürgen; Keese, Reinhart; Eschenmoser, Albert (2015). "Corrin Syntheses. Part V. Preparation of Metal-Free Corrin Derivatives via A→B Ring Closure. Complexation of the Corrin Chromophore with Metal Ions, and Some Properties of the Ligands in Corrin Complexes". Helvetica Chimica Acta. 98 (11–12): 1845–1920. doi:10.1002/hlca.201300064.
- ↑ Fuhrer, Walter (1973). Totalsynthese von Vitamin B12: Der photochemische Weg [Total Synthesis of Vitamin B12: The Photochemical Route] (PDF) (PhD) (in German). ETH Zürich (Promotionsarbeit Nr. 5158). doi:10.3929/ethz-a-000086601. hdl:20.500.11850/131362.
- 1 2 Eschenmoser, Albert; Wintner, Claude (1977). "Natural product synthesis and vitamin B12". Science. 196 (4297): 1410–1420. Bibcode:1977Sci...196.1410E. doi:10.1126/science.867037. PMID 867037.
- ↑ Eschenmoser, Albert (1971). Studies on Organic Synthesis. XXIIIrd International Congress of Pure and Applied Chemistry: special lectures presented at Boston, USA, July 26-30, 1971. Vol. 2. London: Butterworths. pp. 69–106. doi:10.3929/ethz-a-010165162. hdl:20.500.11850/84699. ISBN 0-408-70316-4.
- ↑ Bertele, Erhard; Scheffold, Rolf; Gschwend, Heinz; Pesaro, Mario; Fischli, Albert; Roth, Martin; Schossig, Jürgen; Eschenmoser, Albert (2015). "Corrin Syntheses. Part IV. Synthesis of Corrin Complexes via A→B Ring Closure. Coupling of Hemicorrinoid A/D und B/C Components to Corrin by Imido-ester–Enamine Condensations". Helvetica Chimica Acta. 98 (11–12): 1755–1844. doi:10.1002/hlca.201200342.
- ↑ Yamada, Yasuji; Wehrli, Pius; Miljkovic, Dusan; Wild, Hans-Jakob; Bühler, Niklaus; Götschi, Erwin; Golding, Bernard; Löliger, Peter; Gleason, John; Pace, Brian; Ellis, Larry; Hunkeler, Walter; Schneider, Peter; Fuhrer, Walter; Nordmann, René; Srinivasachar, Kasturi; Keese, Reinhart; Müller, Klaus; Neier, Reinhard; Eschenmoser, Albert (2015). "Corrin Syntheses. Part VI. Corrin Synthesis via A→D Ring Closure. The Construction of A/D-Secocorrin Chromophore Systems by the 'Sulfide Contraction' Method and the Photochemical A/B-Secocorrin→Corrin Cycloisomerization". Helvetica Chimica Acta. 98 (11–12): 1921–2054. doi:10.1002/hlca.201500012.