Dipyrrins, Pyrrolyldipyrrins, Prodigiosenes and Their Complexes

Abstract

Dipyrrins, pyrrolyldipyrrins and prodigiosenes are a closely related series of molecules: pyrrolyldipyrrins are dipyrrins with a pyrrolic substituent and prodigiosenes are a special class of pyrrolyldipyrrins with a methoxy substituent. Prodigiosenes are known for their anticancer activity, but although there have been a number of developments in their synthesis, chemical manipulation of prodigiosenes is rare. Development of a methodology for the chemical manipulation of prodigiosenes would allow a convergent synthesis of a closely related series of prodigiosenes ideal for investigations into structure activity relationships. Chemical manipulation of dipyrrins is also rare, but this is largely overcome by first converting dipyrrins to dipyrrinato complexes. The same strategy could potentially apply to pyrrolyldipyrrins and prodigiosenes, but there are very few known pyrrolyldipyrrinato complexes. Three projects were undertaken in order to investigate the chemical manipulation of dipyrrins and pyrrolyldipyrrins. The first project was to investigate the synthesis of a library of prodigiosenes by way of a convergent approach. The synthesis of a functionalized prodigiosene, with demonstrated anticancer activity, was optimized and many methods for functional group interconversion of an ester attached to the prodigiosene core were investigated. Ultimately, this method was unsuccessful in the synthesis of a library of prodigiosenes due to instability of prodigiosene intermediates. The second project was to investigate the synthesis of pyrrolyldipyrrinato complexes. A series of pyrrolyldipyrrinato tin(IV) complexes with a previously unobserved binding mode for pyrrolyldipyrrins were successfully synthesized and one complex of the series was characterized using x-ray crystallography. Although fluorescent dipyrrinato complexes, with the exception of boron difluoride complexes, are rare, all of the pyrrolydipyrrinato tin(IV) complexes were highly fluorescent with fluorescence quantum yields between 0.28 to 0.61. The third project was to develop a protection method for pyrrolyldipyrrins using dipyrrins as model compounds. A general, high yielding method was developed to remove the BF2 group from a dipyrrinato borondifluoride complex to generate a dipyrrin. Preliminary application of this deprotection methodology to prodigiosene boron difluoride complexes shows promise. This deprotection methodology allowed for the development of a new methodology for the synthesis of meso-alkyl substituted dipyrrins via meso-modification of their corresponding boron difluoride complexes.