Distinguished Professor, Organic Chemistry

B.Sc. (Hon.) 1975, University of Exeter
M.Sc. 1977, University College, Cardiff, Wales
Ph.D. 1979, University College, Cardiff, Wales
Postdoctoral: University of Texas at Arlington,

Email: tdlash@ilstu.edu
Phone: (309)438-8554
Office: 306 Science Laboratory Building

Porphyrins and Related Macrocycles: Nature’s [18]Annulenes
Nature has selected the porphyrin nucleus, generally in metallated form, for a surprising number of functions that include oxygen transportation in mammals (hemoglobin), energy production from O2 reduction as part of the respiratory chain (cytochrome oxidase), electron transport/redox (cytochromes), peroxide breakdown (catalase, peroxidases), photosynthesis (chlorophylls) and so on.

The versatility of this tetrapyrrolic system stems in part from its intrinsic stability and its ability to form chelates with many different transition metals at varying oxidation levels. Porphyrins also represent an unparalleled family of aromatic macrocycles that formally possess [18]annulene characteristics and as such are the only naturally occurring examples of higher bridged annulene structures.

Although the porphyrin system is generally near planar, it can be severely distorted from planarity without significantly sacrificing its aromatic properties. On the other hand, the biological functions of metalloporphyrins are known to be modulated by conformational restrictions within protein environments. Porphyrins and their structural cousins the phthalocyanines show some potential for use as nonmetallic electrical conductors, catalysts and in solar energy conversion. In addition, porphyrin derivatives are presently under clinical trials as photosensitizers for photodynamic tumor therapy. In my laboratory, we are developing new synthetic routes to these important macrocyclic compounds. These projects are directed at the synthesis of both natural systems and unique species with novel spectroscopic and chemical properties. Porphyrins are commonly found in petroleum and other fossil fuels and these compounds are believed to be degradation products, or molecular fossils, of biological pigments such as the chlorophylls. The analysis of petroporphyrins has value both in chemical prospecting and environmental studies (e.g., tracking the origins of oil spills), and our work has provided valuable standards for these studies. In addition, synthetic porphyrin samples have being used as probes for the substrate specificity of the heme biosynthetic enzymes, work that has clinical significance in relation to diseases of porphyrin metabolism. However, the major emphasis of our current investigations involves the synthesis of modified porphyrin structures with fused aromatic rings and/or modified subunits. These studies provide new insights into the nature of aromaticity in these "[18]annulenes of Nature" and have resulted in the discovery of remarkable new chemistry.

SELECTED PUBLICATIONS

L. Xu, G. M. Ferrence and T. D. Lash, "[22]Porphyrin-(3.1.1.3), a new vinylogous expanded porphyrin system", Organic Letters 2006, 8 (22), 5113-5116.

J. A. El-Beck and T. D. Lash, "Tetraphenyloxybenziporphyrin, a new organometallic ligand for silver(III) and gold(III)", Organic Letters 2006, 8 (23), 5263-5266.

L. Xu and T. D. Lash, "Synthesis of aromatic dicarbaporphyrinoids from resorcinol and 2-methyl-resorcinol", Tetrahedron Letters 2006, 47 (50), 8863-8866.

J. M. Manley, T. J. Roper and T. D. Lash, "Synthesis of isomeric angularly annealed dinaphthoporphyrin systems: Examination of the relative positioning and orientation of ring fusion as factors influencing the porphyrin chromophore", Journal of Organic Chemistry 2005, 70 (3), 874-891.

T. D. Lash, "The Enigma of Coproporphyrinogen Oxidase. How Does This Unusual Enzyme Carry Out Oxidative Decarboxylations to Afford Vinyl Groups?", Bioorganic & Medicinal Chemistry Letters 2005, 15 (20), 4506-4509.

T. D. Lash, Y. Lin, B. H. Novak and M. D. Parikh, "Porphyrins with Exocyclic Rings. Part 19. Efficient Syntheses of Phenanthrolinoporphyrins", Tetrahedron 2005, 61 (49), 11601-11614.

C. M. Cillo and T. D. Lash, "Porphyrins with Exocyclic Rings. Part 20. Synthesis and spectroscopic characterization of porphyrins with fused 2,1,3-benzoxadiazole and 2,1,3-benzoselenadiazole moieties", Tetrahedron 2005, 61 (49), 11615-11627.