chlorophyll-b has been researched along with chlorin* in 2 studies
2 other study(ies) available for chlorophyll-b and chlorin
| Article | Year |
|---|---|
Regioselective bromination tactics in the de novo synthesis of chlorophyll b analogues.
The ability to introduce substituents at designated sites about the perimeter of the chlorin or 13(1)-oxophorbine macrocycle is essential for fundamental studies related to chlorophylls. A chlorin is a dihydroporphyrin, whereas a 13(1)-oxophorbine is a chlorin containing an annulated oxopentano ring spanning positions 13 and 15. 13(1)-Oxophorbines bearing auxochromes at the 7-position of the macrocycle are valuable targets given their resemblance to chlorophyll a or b, which contains the 13(1)-oxophorbine skeleton and bears a 7-methyl or 7-formyl group, respectively. A rational route to 7-substituted 13(1)-oxophorbines was developed that relies on a new method for regioselective bromination. Under neutral conditions, a 13-acetyl-10-mesitylchlorin (FbC-M(10)A(13)) undergoes bromination (with 1 molar equiv of NBS in THF) both in ring B (7-position) and at the 15-position (42% versus 28% isolated yield), thereby thwarting installation of the isocyclic ring (ring E, spanning the 13-15 positions). Under acidic conditions (10% TFA in CH(2)Cl(2)), ring B is deactivated, and bromination occurs preferentially at the 15-position (87% yield). The capability for preferential 15-bromination is essential to install the isocyclic ring, after which bromination can be directed to the 7-position of ring B (neutral conditions, 86% yield). The ability to suppress bromination in ring B (under acidic media) has been exploited in syntheses of sparsely substituted analogues of chlorophyll b. The analogues contain a 7-substituent (acetyl, formyl, or TIPS-ethynyl), a 10-mesityl group, and the 18,18-dimethyl group as the only substituents in the 13(1)-oxophorbine skeleton. The three analogues exhibit absorption spectral features that closely resemble those of free base analogues of chlorophyll b. Taken together, the facile access to chlorins and 13(1)-oxophorbines bearing substituents at distinct sites should enable fundamental spectroscopic studies and diverse applications. Topics: Chlorophyll; Halogenation; Porphyrins; Spectrum Analysis; Stereoisomerism; Substrate Specificity | 2009 |
Demetalation kinetics of natural chlorophylls purified from oxygenic photosynthetic organisms: effect of the formyl groups conjugated directly to the chlorin pi-macrocycle.
Demetalation kinetics of natural chlorophyll (Chl) d purified from Acaryochloris marina was first studied and compared with those of Chls a and b. The demetalation rate constant of Chl d, which possessed a formyl group at the 3-position, was five-fold smaller than that of Chl a possessing a vinyl group at the same position in aqueous acetone at the proton concentration of 1.2 x 10(-3) M at 25 degrees C. In contrast, the demetalation rate constant of Chl b possessing a formyl group at the 7-position was 26 times smaller than that of Chl a. The activation energy of demetalation reaction of Chl d was larger than that of Chl a, but smaller than that of Chl b. These indicate that the substitution effect of 3-formyl group on the acidic removal of central magnesium in Chls was smaller than that of 7-formyl group. Topics: Chlorophyll; Chlorophyll A; Cyanobacteria; Kinetics; Magnesium; Photosynthesis; Porphyrins; Spectrophotometry | 2009 |