A collaborative paper between the Birge, Gascon, and our group, led by Matthew Guberman-Pfeffer, reporting on a novel and unique mechanism to red-shift bacteriochlorin chromophores was accepted for publication as a full paper in the J. Am. Chem. Soc.!

While our ‘breaking and mending’ of porphyrin strategy proved versatile over the last decade in the generation of a range of pyrrole-modified porphyrins containing 4-, 5-, and 6-membered heterocycles, it failed to access systems incorporating larger rings. A reversal of the strategy – first mending, then breaking – now allowed the formation of a pyrrole-modified porphyrin containing an 8‑membered 1,3,6-triazocine-2,4,8-trione heterocycle. Mike Luciano and Wes Tardie continue working on the generalization of this strategy.

Luciano, M.; Tardie, W.; Zeller, M.; Brückner, C. ‘Supersizing Pyrrole-modified Porphyrins by Reversal of the ‘Breaking and Mending’ Strategy’ Chem. Commun. 2016, 52, 10133-10136.

Congratulations, Meenakshi’s and Eileen’s paper on the ozonation of octaalkylporphyrins was published in Chem.–Eur. J.!

Sharma, M.; Meehan, E.; Mercado, B. Q.; Brückner, C. ‘Oxazolochlorins 16. b‑Alkyloxazolo­chlorins: Revisiting the Ozonation of Octaalkylporphyrins, and Beyond’ Chem.–Eur. J. 2016, 22, 11706–11718.

Syntheses and optical properties of mono- and bis-chromene-annulated meso-arylbacteriochlorins are described. Bacteriochlorins are red and NIR light absorbing chromophores of potential utility in synthetic light harvesting and biomedical applications as photochemotherapeutics or labelling dyes. The report expands the body of work on the optical fine-tuning of synthetic meso-aryl-substituted bacteriochlorins through intramolecular annulation reactions. The regiochemical outcomes of these annulation reactions were investigated using computational tools.  (Hyland, M. A.; Hewage, N.; Panther, K.; Nimthong-Roldán, A.; Zeller, M.; Samaraweera, M.; Gascón, J. A.; Brückner, C. ‘Chromene-annulated Bacteriochlorins’ J. Org. Chem. 2016, accepted for publication 4/14/2016)

Over the past 15 years, our group developed the ‘Breaking and Mending’ strategy of converting porphyrins to porphyrin analogs containing non-pyrrolic building blocks, and this work has become the mainstay of our current work. In the Accounts of Chemical Research paper (Brückner, C. ‘The Breaking and Mending of meso-Tetraarylporphyrins: Transmuting the Pyrrolic Building Blocks’ Acc. Chem. Res. 2016, 49, 1080−1092.), the strategy was summarized and diversity of structures accessible is highlighted. An artistic representation of the concept is gracing the issue No 6 of the Accounts!

A paper describing the expansion of a pyrrolic building block in meso-tetraphenylporphyrins by a nitrogen atom generating pyrazinoporphyrins was finally published (Eur. J. Org. Chem. 2016, DOI: 10.1002/ejoc.201501436)! The work goes back to 2000, when CB himself still worked in the lab and made the stable nickel complexes, but he was never able to make the much trickier to make but more interesting free base derivatives. This was accomplished by Michelle Head (neé Dean), PhD 20011 (her pyrazinoporphyrin syntheses were done in 2007-2008), and Gloria Zarate, M.S. 2010! Good things sometimes take a long while!

This paper presents the first structural model of the oxidation products of biliverdin. Biliverdin dimethyl ester, extracted from Emu eggshells, was shown to be oxidized by singlet oxygen, and the oxidation products were structurally characterized. While the role of biliverdin as a biological antioxidant is long known (albeit its role is Emu eggshells may simply be as a color to camouflage the eggshell from predators) and its reactivity with singlet oxygen was also shown before, the nature of the reaction products remained hitherto unknown.  Thus, this study helps to understand the molecular mechanism of the antioxidant action of biliverdin.

Dorazio, S.; Halepas, S.; Fleming, K. M.; Zeller, M.; Bruhn, T.; Brückner, C. ‘Singlet Oxygen Addition Products of Biliverdin IXα Dimethyl Ester’ Bioorg. Med. Chem. 2015, 23, 7671–7675 (DOI:10.1016/j.bmc.2015.11.012).

For Sarina’s AudioSlide presentation of the papers, see:

Indaphyrins, pyrrole-modified porphyrins containing a cleaved pyrrole β,β’-bond and two annulated indanone moieties, possess unusually broadened and redshifted UV/Vis spectra because of their π-expanded chromophores. Its free base has been crystallographically characterized, highlighting its strongly ruffled conformation incorporating a helimeric twist. Free base indaphyrin was shown to be susceptible to regiospecific derivatizations at the opposite side of the ring-cleaved pyrrole (dihydroxylation, followed by functional group transformations of the resulting diol functionality), generating indaphyrin-based chlorin analogues, indachlorins, that incorporate a dihydroxypyrroline, pyrrolindione, oxazolone, or a morpholine moiety. Structural modifications resulted in further broadening and hyper- and bathochromic shifts of the optical spectra, some of which possess a nearly panchromatic absorption between 300 to well above 900 nm. The extents to which these modifications affect their solid-state conformations were analyzed:

Samankumara, L.; Dorazio, S.; Akhigbe, J.; Li, R.; Nimthong-Roldán, A.; Zeller, M.; Brückner, C. ‘Indachlorins: Nonplanar Indanone-Annulated Chlorin Analogues with Panchromatic Absorption Spectra Between 300 and 900 nm’ Chem.–Eur. J. 2015, accepted for publication.