De NovoSynthesis of Gem-Dialkyl Chlorophyll Analogues for Probing and Emulating Our Green World

Abstract

Woodward reported his infamous synthesis of chlorin e 6 trimethyl ester, a known synthetic precursor to chlorophyll a. [59][60][61][62][63][64]124 The work was posited on a half-century of intensive studies by many investigators in tetrapyrrole chemistry and began a decade after the close of Fischer's lifetime of research 125−128 (which included an uncompleted synthetic program directed toward chlorophylls 15 ). Indeed, "he read all the umpteen papers on the chlorophylls written by Willstaẗter and Fischer, including the experimental parts." 129 The Woodward synthesis of chlorin e 6 trimethyl ester required 46 steps, of which 24 were spent on converting the sole precursor, Knorr's pyrrole, to the four pyrroles destined to form rings A−D; 7 additional steps accrued to obtain the dipyrromethanes that constitute the Eastern and Western halves (Scheme 13, the step numbers are identical to those shown in ref 64.). The first step formed the Knorr pyrrole (in several kg quantities), the next 24 steps were divided into four parallel paths, whereas the remaining 21 steps proceeded in linear fashion. Remarkable features of the synthesis include the directed intramolecular joining (via an imine) of the Eastern and Western halves (step 33), construction of the acrylate Scheme 10. Hydrogenation of a Porphyrin to Form a Chlorin Scheme 11. Representative meso-Tetraarylchlorins Scheme 12. Methyl Pyropheophorbide a

Bioconjugatable, PEGylated hydroporphyrins for photochemistry and photomedicine. Narrow-band, red-emitting chlorins

“…15 Each synthetic chlorin bears a geminal dimethyl group in the reduced, pyrroline ring to block adventitious dehydrogenation (Chart 4). Tuning the position of the long-wavelength (Q y ) absorption band can be accomplished chiefly by (1) introduction of auxochromes at positions along the y-axis (i.e., the β-pyrrole positions 2, 3, 12 and 13 in rings A and C), and (2) metalation, and to lesser extent by (3) introduction of auxochromes at positions along the x-axis (i.e., the β-pyrrole positions 7 and 8, and the β-pyrroline position 17) in rings B and D. Given the desire to exploit the β-pyrrole positions for wavelength tuning, a water-solubilization motif and a bioconjugatable tether are ideally installed at positions 5 and 15.…”

Synthesis and Oxidation of Internally Chlorinated Carbachlorins

“…been reported, but in every case low to moderate yields were obtained. As is the case for tetrapyrrolic chlorins, [23,24] carbachlorins show moderately strong absorptions at 650 nm or higher, a feature that could find applications in photodynamic therapy. [25] Carbachlorins are also more stable than their tetrapyrrolic counterparts as they require more stringent conditions in order for oxidation to carbaporphyrin to occur.…”

Transformations of meso‐Iminofunctionalized Pd(II) and Ni(II)‐Complexes of β‐Alkylsubstituted Porphyrins

“…Compounds (1-2), (5-8), (9-10), (11)(12)(13)(14) were synthesized according to reported procedures. [33,34,46] Compounds (15), (16) were obtained from commercial sources.…”

“…In particular, metal complexes of porphyrins form the basis of the photosynthetic center, transfer oxygen (hemoglobin), catalyze oxidative processes as part of enzymes (cytochromes). [13,14] One of the most important directions of modification of porphyrins and their derivatives is the formyl group insertion into various positions of the macro-porphyrin were obtained by treatment of the corresponding meso-imino derivatives with bases. Photophysical characteristics of porphyrins and their analogues allow to successfully use these dyes as fluorescent/phosphorescent sensors in bioanalysis, [1][2][3][4][5][6] photosensitizers in photovoltaics, [7,8] photocatalysis [9,10] and photodynamic therapy of tumors [2,4] and other diseases (acne, psoriasis, atherosclerosis).…”