Stereochemistry and Chiroptic Properties of Pheophorbides and Related Compounds*

Wolf, H.; Scheer, Hugo

doi:10.1111/j.1749-6632.1973.tb43236.x

Cited by 35 publications

(27 citation statements)

References 45 publications

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“…31a The ORD/CD spectra of pheophorbides are comparably insensitive to the relative configuration of C-7 and C-8, but the sign of the major π-π* transitions is determined by the absolute configuration at C-7. This striking feature has been interpreted in terms of an inherently dissymmetric chromophore 130 (see above).…”

Section: B Metallochlorinsmentioning

confidence: 99%

“…130 10-Alkoxymethylpheophorbides are configurationally stable under most conditions. They were, therefore, investigated in some detail to evaluate the chiroptical and 1 H nmr properties of the pure C-10 epimers.…”

Section: Configurational Stabilitymentioning

confidence: 99%

“…43,[133][134][135] The basic features of the ORD/CD spectra are determined by the chirality of C-7, while substituents and chirality of the asymmetric C-8, 9, and 10 yield incremental contributions superimposed on the spectrum of the inherently dissymmetric chromophore. 130 The increased flexibility of the reduced ring D was first demonstrated by Ή nmr studies of δ-substituted chlorins. 129^143^144 Introduction of a bulky substituent into this position in pheophorbides leads to pronounced incre mental chemical shifts of proton resonances arising from ring D substituents, Fig.…”

Section: A the Macrocyclementioning

confidence: 99%

“…Both methods can be used independently and were recently reviewed. 3,130 The same methods that have been used to link the stereochemistry at C-10 with that at C-7 and C-8 can be used to link the stereochemistry of C-9 with that at C-10. In the chlorophylls, C-9 is sp 2 hybridized and, thus, achiral.…”

Section: B Metallochlorinsmentioning

confidence: 99%

“…2). This is indicated from the chiroptic proper ties of pheophorbides, 130 and reflected in the X-ray analysis. 43,[133][134][135] The basic features of the ORD/CD spectra are determined by the chirality of C-7, while substituents and chirality of the asymmetric C-8, 9, and 10 yield incremental contributions superimposed on the spectrum of the inherently dissymmetric chromophore.…”

Section: A the Macrocyclementioning

confidence: 99%

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Synthesis and Stereochemistry of Hydroporphyrins

Scheer¹

1978

The Porphyrins

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Section: B Metallochlorinsmentioning

confidence: 99%

Section: Configurational Stabilitymentioning

confidence: 99%

Section: A the Macrocyclementioning

confidence: 99%

Section: B Metallochlorinsmentioning

confidence: 99%

Section: A the Macrocyclementioning

confidence: 99%

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Synthesis and Stereochemistry of Hydroporphyrins

Scheer¹

1978

The Porphyrins

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Steric interaction between the peripheral substituents of 10(S)‐chlorophyll derivatives and its conformational consequences: A proton magnetic resonance study

Hynninen

Lötjönen

1985

Magnetic Reson in Chemistry

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The improved methods developed recently for the preparation of lo(@-chlorophyll derivatives have permitted a detailed comparison of their conformations with those of the corresponding 10(R) derivatives, utilizing ' H NMR spectroscopy. Starting from the highly purified lo(@ derivative and following its conversion to the corresponding 10(R) form by repeated ' H NMR spectral measurements in acetone-&, reliable values for the differences in the chemical shifts (As) for each epimeric pair of compounds have been obtained. The relatively large A8 values (0.1-0.2ppm) observed for the P-l-CH,, P-H-2, P-3a-CH3 and 10b-CH3 signals were interpreted as indicating the proximity of the C-10 methoxycarbonyl group and the olefinic region of the phytyl group in the lo(@ derivatives. The proximity between these side-chains was considered to be derived principally from the three closely spaced carbonyls in the lo(@ derivatives. To miniize repulsion among the carbonyls, the C-7 and C-10 side-chains presumably assume conformations allowing maximal mutual distances for the carbonyls. As a compromise of various energetic factors, the phytyl group takes up a conformation where it bends to the right hand side of the macrocycle, or above rings V and III. This results in steric crowding between the olefinic region of the phytyl group and the C-10 methoxycarbonyl group. In addition, the other chemical shift increments show that the steric crowding between the bulky side-chains of the lo(@ derivatives increases the steric strain at the periphery of the macrocycle, relieved by pronounced conformational changes in rings IV and V and, to a lesser extent, also in the whole phorbin ring. The conformational differences were found to be larger for the magnesium-free epimers than for the chlorophylls. In the former case, they were also manifested by relatively large A6 values (0.1-0.5 ppm) for the pyrrole NH protons.

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