title: Synthesis of methyl (13(2)R/S)-alkyl-pyropheophorbide a and a non-epimerized chlorophyll a mimic.
abstract: The (13(2)R/S)-methoxycarbonyl group of methyl pheophorbides a/a' (chlorophyll a/a' derivatives) was converted to methyl, ethyl, propyl, and isopropyl groups through the C13(2)-alkylation under basic conditions followed by pyrolysis in 2,4,6-collidine with lithium iodide. All the resulting products, methyl 13(2)-alkyl-pyropheophorbides a, predominantly gave the (13(2)R)-stereoisomers with about one tenth of the (13(2)S)-epimers. Their stereochemistry was determined by 1D/2D NMR and their optical properties were characterized by visible absorption and circular dichroism spectroscopy. Methyl (13(2)R)-propyl-pyropheophorbide a was converted to (13(2)R)-propyl-pyrochlorophyll a by ester exchanging and magnesium chelating reactions. The synthetic chlorophyll a analogue showed non-epimerization at the 13(2)-position in pyridine-d5 at 40°C, while naturally occurring chlorophyll a was easily epimerized under the same conditions to give its epimeric mixture.
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
authors.forename: Shin
authors.initials: S
authors.lastname: Ogasawara
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan. Electronic address: tamiaki@fc.ritsumei.ac.jp.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
mesh_terms: D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D000077194:Chlorophyll A; D008958:Models, Molecular; D015394:Molecular Structure
chemical_list: D002734:Chlorophyll; C040298:pyropheophorbide a; D000077194:Chlorophyll A
keywords: Chlorophyll; Epimerization; Pyrolysis; Stereochemistry