Expanding the Eggshell Colour Gamut!

Bird eggshells just became more colorful! For well over 100 years, only two pigments have been identified in avian eggshells: rusty-brown protoporphyrin (e.g., brown chicken eggs) and blue-green biliverdin (e.g., turquois eggs of robins). However, tinamou (chicken-like forest dwellers of South America) eggshells display unusually colored eggshells, suggesting the presence of other pigments. The Brückner group, in collaboration with the ornithologists and eggshell and bird color experts Daniel Hanley (Long Island University) and Richard Prum (Yale University), investigated this. Through extraction, derivatization, spectroscopy, chromatography, and mass spectrometry, they identified two novel eggshell pigments: yellow–brown bilirubin and red–orange uroerythrin from the guacamole-green and purplish-brown eggshells of two tinamous species. Both pigments are known porphyrin catabolites and were found in the eggshells in conjunction with biliverdin. A colour mixing model using the new pigments and biliverdin reproduced the respective eggshell colours. These discoveries expand our understanding of how eggshell colour diversity is achieved. The ability of these pigments to photo-degrade may have an adaptive value for the tinamous – this is the subject of follow-up studies for the ornithologists.

Hamchand, R.; Hanley, D.; Prum, R.O.; Brückner, C. ‘Expanding the Eggshell Colour Gamut: Uroerythrin and Bilirubin from Tinamou (Tinamidae) Eggshells’ Sci. Rep. 202010, 11264.

3-Part Series in Eur. J. Org. Chem. is out!

The 3-part series of papers study on the ring expansion reactions of the octaethyloxochlorins “Surprising Outcomes of Classic Ring Expansion Conditions Applied to Octaethyloxochlorin” is out (Part 1. Baeyer-Villiger Oxidation Conditions’ Eur. J. Org. Chem. 2017, 1820–1825. Part 2. Beckmann Rearrangement Conditions. Eur. J. Org. Chem. 2017, 1826–1834, and Part 3. Schmidt Reaction Conditions). All contributions were led by Ruoshi Li, the crystal structures were provided by Matt Zeller, and the Part 2 is the full paper of the work began by Eileen Meehan. The series was also highlighted by a cover page. We learn from this work that hardly anything goes as planned in porphyrin chemistry!

Mending and Breaking Manuscript Published in Chem. Commun.

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.

Journal of Organic Chemistry Manuscript Accepted

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)

Accounts of Chemical Research paper accepted for publication

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. 201649, 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!

Pyrazinochlorins – at long last

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!

Biliverdin oxidation paper is published

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:

Indachlorins: Chlorin Analogues with Panchromatic Absorption Spectra Between 300 and 900 nm

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.