biliverdin-IXα Dimethyl Ester Research Articles

Singlet oxygen oxidation products of biliverdin IXα dimethyl ester

Biliverdin IXα is a naturally occurring linear tetrapyrrolic product of the enzymatic oxidative ring cleavage of heme. Evidence is mounting that biliverdin possesses antioxidant properties in mammals but its mode of action is unclear. We present the single crystal X-ray structure analysis of two regioisomeric biladien-1,19-diones-ab that are derived from biliverdin IXα dimethyl ester by addition of two vicinal trans-methoxy groups to the 4,5- or 15,16-double bonds, respectively. The compounds were likely formed by photosensitized singlet oxygen addition, followed by Lewis acid-catalyzed methanol-induced ring-opening of the intermediate epoxide, and OH-to-OMe substitution. We thus present structural evidence for a possible reaction mechanism by which biliverdin can act as an antioxidant.

Phenyl biliverdin isomers obtained by chemical oxidation of iron(III) complex of 5-phenyl protoporphyrin IX

Oxidative cleavage of synthetic 5-phenyl protohemin IX in pyridine solution in the presence of ascorbic acid (coupled oxidation), followed by esterification of the products with boron trifluoride-methanol rendered mainly three isomeric biliverdins. These were identified by MS and 1D and 2D1H NMR as 15-phenyl biliverdin IXβ (1), 10-phenyl biliverdin IXγ (2) and 5-phenyl biliverdin IXδ (3) dimethyl esters. The fact that biliverdin IXα dimethyl ester derivative is not obtained indicates that oxidation fails to occur in the α-meso-carbon bearing the phenyl group.

Novel reaction modes of biliverdin-IXα: synthesis and structure of bilatriene dimers

Novel reactions of biliverdin-IXα dimethyl ester 2 affording compounds carrying two bilatriene entities are reported. Thus compound 2 undergoes various acid-promoted dimerisations by regio-and site-selective reaction of the respective vinyl groups adjacent to the pyrrolinone carbonyls to give the cyclobutane, 4, the diastereoisomeric cyclohexenes 5a and 5b, the butene 6 and its corresponding methanol adducts 7a and 7b. The distribution of products can be controlled by varying the concentration of acid and temperature. The elucidation of structure, stereochemistry and conformation of the compounds synthesised is accomplished mainly using spectroscopic means. The 1,2-trans relation of the two biliverdin moieties in the cyclobutane 4 is established by an asymmetric synthesis. The mechanism of reactions and the differences in the reactivity of the two vinyl groups in compound 2 and other biliverdins are discussed.

Geometry versus basicity of bilatrienes: Stretched and helical protonated biliverdins

The ease of protonation of bilatrienes at the pyrrolenine nitrogen critically depends on their conformation. The biliverdin2 being constrained to a helical (Z, Z, Z, syn, syn, syn) geometry by its four link chain is ca. three orders of magnitude less basic than flexible open-chain bilatrienes like biliverdin-IXα dimethyl ester (1), which is shown to adopt a stretched conformation in its monoprotonated form. These results are obtained by a comparative investigation of the titrations of1 and2 with sulfuric acid in methanol and methanol-water by means of UV-VIS and NMR spectroscopy.

ChemInform Abstract: Spectroscopy and Reactivity of Zinc 20‐Oxaporphyrin‐IX Dimethyl Ester.

A facile method of preparing zinc 20-oxaprotoporphyrin-IX dimethyl ester (1) from biliverdin-IXα dimethyl ester has been found. According to NMR spectroscopy, the oxa substituent has a pronounced influence on the properties of the macrocyclic ring system. The 1H NMR spectrum reveals an aromatic structure and 13CNMR shows that in 1 a positive charge is delocalized, in agreement with the presence of one positive charge, and further that C-1 and C-19 have acquired the highest positive charge. This is corroborated by the reaction with nucleophiles, especially thiolates, leading to isolated adducts which could be well characterized. The adducts are the result of nucleophilic attack on the positions 1 and 19 exclusively, which agrees well with the charge on these positions in 1. The adducts show interesting spectroscopic properties. The study of oxaporphyrins and their nucleophilic adducts may contribute to a fuller understanding of the formation and properties of bile pigments.

Cyclization of biliverdins to verdohaemochromes

Iron(II) octaethylverdohaemochrome was obtained both by cyclization of octaethylbiliverdin in the presence of FeSO4 and pyridine, and by coupled oxidation of octaethylhaemin and ascorbic acid with O2 in the presence of pyridine. The compound obtained by cyclization of biliverdin IXα dimethyl ester was, however, different from that obtained by the methylation of iron(II) protoverdohaemochrome IXα, the product of coupled oxidation of the protohaem in myoglobin. The electronic absorption spectra of the pyridine and tosylmethyl isocyanide (TsCH2NC) complexes, (14) and (15), of the product of cyclization were different from the spectra of the same complexes, (11) and (12), of the product of coupled oxidation. The product of cyclization was reduced to the product of coupled oxidation by sodium dithionite. It is postulated that compounds (14) and (15) are bis(pyridine) and bis(isocyanide) co-ordination complexes of iron (III) protoverdohaemochrome dimethyl ester. The positions of the maxima in the absorption spectra of compounds (16) and (17), the pyridine and TsCH2NC complexes of both the product of coupled oxidation of mesohaemin dimethyl ester and the product of cyclization of mesobiliverdin dimethyl ester, indicated that these compounds are analogues, not of (11) and (12), but of (14) and (15). Iron(II) azaporphyrins (7) and (13) were prepared by treatment of the corresponding iron(II) oxaporphyrins (5) and (11) with ammonia.

Presence of biliverdin IX.ALPHA. in the gallbladder bile of red sea bream.

The gallbladder bile of red sea bream Pagrus major was analyzed by TLC and HPLC.TLC pattern shows only one blue band and some yellow bands. Pigments extracted from blue band were analyzed by HPLC. Two peaks appeared. Judging from the absorbance at 365 and 436 nm and the retention time, the pigment in first minor peak may be bilirubin diglu-curonide. The retention time of second major peak was equal to that of biliverdin IXα. The blue pigment in second peak was reduced with NaBH4 and analyzed by HPLC. The retention time of reduced pigment was same as that of bilirubin IXα. The blue pigment was methylated with BF3-methanol and analyzed by HPLC. The retention times of methylated pigment and biliverdin IXα dimethylester were the same. These results indicate that the blue pigment is biliverdin IXα and only biliverdin IXα exists as verdinoids in the bile of red sea bream.

Bile pigment studies-VII New syntheses of biliverdin-IXα dimethyl ester and two related mono-vinyl-mono-ethyl isomers

Using the recently developed route through di-t-butyl b-bilene-1,19-dicarboxylates, new syntheses of biliverdin-IXα dimethyl ester ( 1) and two related mono-vinyl-mono-ethyl isomers ( 2) and ( 3), are described. The two dihydro-derivatives of ( 1) are important in connection with biosynthetic studies of the origin of algal biliproteins.

Picosecond Kinetics of Excited State Relaxation in Biliverdin Dimethyl Ester

AbstractThe relaxation processes of biliverdin IXα dimethyl ester have been studied by time‐resolved absorption and fluorescence detection, using pump‐probe and single‐photon timing techniques, respectively. The results complement and extend those of earlier investigations.1,3–5 In 2‐methyltetrahydrofuran, chloroform, ethanol, and ethyl lactate, four emitting species, two short‐lived (picosecond) and two long‐lived ones (nanosecond), have been detected. In methanol, the number of emitters is possibly reduced to three. In the cases of four emitters, these can be attributed to either three or four ground state forms. We conclude that the radiationless relaxation of the short‐lived excited states is simultaneously induced both by proton transfer processes and by conformational changes, as previously discussed.3 The spectroscopic properties of the long‐lived species point to the presence of relatively rigid conformations of the bilatriene in liquid solutions at room temperature. The possible relevance of this observation with regard to the influence of protein interactions on the conformational equilibrium of tetrapyrroles in phycobiliproteins is discussed.

Singlet oxygen reactivity of bilirubin and related tetrapyrroles

The rates of chemical reactivity (kR) and physical quenching (kQ) of singlet oxygen by bilirubin IXα, mesobilirubin IXα, bilirubin IXα dimethyl ester, aetiobilirubin IVγ, biliverdin IXα, biliverdin IXα dimethyl ester, aetiobiliverdin IVγ and an oxodipyrromethene have been determined. The kR and kQ values approach the diffusion threshold for the bilirubin-like substrates, but kR<kQ by about a factor of 103 for the verdins. A reaction mechanism involving superoxide ion is suggested. Bilirubin appears to quench singlet oxygen by an electron-transfer mechanism.

Evidence for singlet oxygen quenching by biliverdin IX-α dimethyl ester and its relevance to bilirubin photo-oxidation

Summary Biliverdin IX-α dimethyl ester inhibits the sensitized and unsensitized photo-oxidation of bilirubin IX-α. Biliverdin IX-α is probably not an intermediate in the main pathway of bilirubin photo-oxidation in vitro .