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Monatshefte fur chemie

Intramolecular Hydrogen Bonding and Linear Pentapyrrole Conformation.


PMID 25110361

Abstract

Three new linear pentapyrrole rubinoid analogs: 2,3,7,8,17,18,22,23-octamethyl-12,13-bis-(2-carboxyethyl)-1,10,15,24,25,27,28,29-octahydro-27H-pentapyrrin-1,24-dione and 2,3,8,12,13,17,22,23-octamethyl-7,18-bis-(2-carboxyethyl)-1,10,15,24,25,26,27,28,29-octahydro-27H-pentapyrrin-1,24-dione, and its 7,18-dihexanoic acid analog were synthesized, respectively, from 2,3,7,8-tetramethyl-(10H)-dipyrrin-2-one, from 2,3,8-trimethyl-7-[2-(methoxycarbonyl)ethyl]-(10H)-dipyrrinone, and 2,3,8-trimethyl-7-[5-(methoxycarbonyl)pentyl]-(10H)-dipyrrinone. (13)C NMR and (1)H NMR measurements in (CD3)2SO confirmed the pentapyrrole structures, while (1)H NMR data indicate intramolecular hydrogen bonding between the CO2H and dipyrrinone groups. Molecular mechanics modeling studies suggest stable U-shape conformations capable of encapsulating small planar aromatic molecules.