Biliverdin Derivatives Research Articles

Electrosynthesis of Verdoheme and Biliverdin Derivatives Following Enzymatic Pathways.

Artificial syntheses of biologically active molecules have been fruitful in many bioinspired catalysis applications. Specifically, verdoheme and biliverdin, bearing polypyrrole frameworks, have inspired catalyst designs to address energy and environmental challenges. Despite remarkable progress in benchtop synthesis of verdoheme and biliverdin derivatives, all reported syntheses, starting from metalloporphyrins or inaccessible biliverdin precursors, require multiple steps to achieve the final desired products. Additionally, such synthetic procedures use multiple reactants/redox agents and involve multistep purification/extraction processes that often lower the yield. However, in a single step using atmospheric oxygen, heme oxygenases selectively generate verdoheme or biliverdin from heme. Motivated by such enzymatic pathways, we report a single-step electrosynthesis of verdoheme or biliverdin derivatives from their corresponding meso-aryl-substituted metalloporphyrin precursors. Our electrosynthetic methods have produced a copper-coordinating verdoheme analog in >80% yield at an applied potential of 0.65 V vs ferrocene/ferrocenium in air-exposed acetonitrile solution with a suitable electrolyte. These electrosynthetic routes reached a maximum product yield within 8 h of electrolysis at room temperature. The major products of verdoheme and biliverdin derivatives were isolated, purified, and characterized using electrospray mass spectrometry, absorption spectroscopy, cyclic voltammetry, and nuclear magnetic resonance spectroscopy techniques. Furthermore, X-ray crystallographic data were collected for select cobalt (Co)- and Cu-chelating verdoheme and metal-free biliverdin products. Electrosynthesis routes for the selective modification at the macrocycle ring in a single step are not known yet, and therefore, we believe that this report would advance the scopes of electrosynthesis strategies.

Oxidative ring-openings of octaethyl-2-oxochlorin: Regioisomeric β-oxobiliverdins

We describe the oxidative ring opening of octaethyl-2-oxochlorin using two different oxidation methods, both providing a mixture of all possible regioisomeric products (8-[Formula: see text] through 8-[Formula: see text]. While isomers 8-[Formula: see text], 8-[Formula: see text], and 8-[Formula: see text] formed in isolable yields and relative ratios that varied with the oxidation method used, isomer 8-[Formula: see text] was invariably formed in trace amounts only. The three major products were spectroscopically characterized (IR, MS, 1D- and 2D NMR spectroscopy) and their configurations were deduced by NMR spectroscopy. The spectroscopic findings correlated well with the single crystal X-ray structure of the novel cleavage product 8-[Formula: see text] and the known compound of 8-[Formula: see text]. The work broadens the number of octaethylporphyrin-derived biliverdin derivatives available and presents a methodology of controlling the biliverdin backbone configuration by introduction of a [Formula: see text]-ketone functionality into select positions.

Supplementation with Phycocyanobilin, Citrulline, Taurine, and Supranutritional Doses of Folic Acid and Biotin-Potential for Preventing or Slowing the Progression of Diabetic Complications.

Oxidative stress, the resulting uncoupling of endothelial nitric oxide synthase (eNOS), and loss of nitric oxide (NO) bioactivity, are key mediators of the vascular and microvascular complications of diabetes. Much of this oxidative stress arises from up-regulated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. Phycocyanobilin (PhyCB), the light-harvesting chromophore in edible cyanobacteria such as spirulina, is a biliverdin derivative that shares the ability of free bilirubin to inhibit certain isoforms of NADPH oxidase. Epidemiological studies reveal that diabetics with relatively elevated serum bilirubin are less likely to develop coronary disease or microvascular complications; this may reflect the ability of bilirubin to ward off these complications via inhibition of NADPH oxidase. Oral PhyCB may likewise have potential in this regard, and has been shown to protect diabetic mice from glomerulosclerosis. With respect to oxidant-mediated uncoupling of eNOS, high-dose folate can help to reverse this by modulating the oxidation status of the eNOS cofactor tetrahydrobiopterin (BH4). Oxidation of BH4 yields dihydrobiopterin (BH2), which competes with BH4 for binding to eNOS and promotes its uncoupling. The reduced intracellular metabolites of folate have versatile oxidant-scavenging activity that can prevent oxidation of BH4; concurrently, these metabolites promote induction of dihydrofolate reductase, which functions to reconvert BH2 to BH4, and hence alleviate the uncoupling of eNOS. The arginine metabolite asymmetric dimethylarginine (ADMA), typically elevated in diabetics, also uncouples eNOS by competitively inhibiting binding of arginine to eNOS; this effect is exacerbated by the increased expression of arginase that accompanies diabetes. These effects can be countered via supplementation with citrulline, which efficiently enhances tissue levels of arginine. With respect to the loss of NO bioactivity that contributes to diabetic complications, high dose biotin has the potential to “pinch hit” for diminished NO by direct activation of soluble guanylate cyclase (sGC). High-dose biotin also may aid glycemic control via modulatory effects on enzyme induction in hepatocytes and pancreatic beta cells. Taurine, which suppresses diabetic complications in rodents, has the potential to reverse the inactivating impact of oxidative stress on sGC by boosting synthesis of hydrogen sulfide. Hence, it is proposed that concurrent administration of PhyCB, citrulline, taurine, and supranutritional doses of folate and biotin may have considerable potential for prevention and control of diabetic complications. Such a regimen could also be complemented with antioxidants such as lipoic acid, N-acetylcysteine, and melatonin—that boost cellular expression of antioxidant enzymes and glutathione—as well as astaxanthin, zinc, and glycine. The development of appropriate functional foods might make it feasible for patients to use complex nutraceutical regimens of the sort suggested here.

NADPH Oxidase Activity in Retinal Pigmented Epithelium as a Target for Prevention of Age-related Macular Degeneration

Considerable evidence points to macular oxidative stress as a key driver of age-related macular degeneration (AMD). In particular, retinal pigmented epithelial (RPE) cells subjected to oxidative stress are prone to apoptosis or senescence; lose their tight junctions; decrease their production of factors which provide trophic support for retinal photoreceptors, suppress choroidal neovascularization, and control complement activation; and boost their production of vascular endothelial growth factor (VEGF), a major stimulant to neovascularization – all effects which are consistent with the pathogenesis of AMD. There is good reason to suspect that NADPH oxidase activity in RPE cells is the key source of the oxidative stress that compromises RPE function in AMD. Studies with other cell lines indicate that a number of risk factors for AMD – including cigarette smoke, homocysteine, hyperglycemia, cadmium, and up-regulated activation of the alternative complement cascade – have the ability to stimulate NADPH oxidase activity, as does all-trans-retinal, a suspected pathogenic factor in AMD. Hence, measures which can down-regulate NADPH oxidase activity may have potential for preventing or controlling AMD. These may include high-dose statins – found to reverse features of early AMD in about half of patients in a recent pilot study – and spirulina, a rich source of the chromophore phycocyanobilin (PhyCB ). PhyCB is a biliverdin derivative that can mimic the intracellular physiological role of bilirubin as an NADPH oxidase inhibitor. Patients with Gilbert syndrome or relatively high plasma unconjugated bilirubin may be at lower risk for AMD owing to bilirubin’s inhibitory impact on NADPH oxidase; this prediction could be readily tested in epidemiological studies.

Total Synthesis of Doubly Locked 5Za15Ea-Biliverdin Derivative: A Convergent Synthesis of theE-antiDipyrrole Component Locked with a 7-Membered Ring

Doubly locked 5Za15Ea-biliverdin (BV) derivative was synthesized toward the investigation of stereochemistry and function of the Pfr-form chromophore in bacteriophytochromes. A convergent synthetic method was established for the locked E-anti dipyrrole component with a 7-membered ring.

Total Syntheses of Sterically Locked Phycocyanobilin Derivatives Bearing a 15Z-anti or a 15E-anti CD-Ring Component

Abstract Total syntheses of sterically locked phycocyanobilin derivatives with a 15Z-anti or a 15E-anti CD-ring component were performed toward elucidation of the stereochemistry and function of the chromophore in phytochromes. In the course of the construction of a sterically locked 15E-anti CD-ring component employing 5-tosylpyrrolin-2-one derivatives as the D-ring, the Ts group was found to be rearranged under acidic conditions to give a mixture of regioisomers, both of which could be transformed into the same CD-ring precursor via detosylation with a base followed by Wittig-like coupling reaction. In addition, a sterically locked 15E-anti biliverdin derivative was also synthesized.

Synthesis of Doubly Locked 5Zs15Za-Biliverdin Derivatives and Their Unique Spectral Behavior

Abstract Doubly locked 5Zs15Za-biliverdin (BV) derivatives were synthesized toward the investigation of stereochemistry and function of the chromophore in bacteriophytochromes. The unique spectral behavior of the doubly locked 5Zs15Za-BV derivatives was observed by UV–vis spectroscopy.

ChemInform Abstract: Total Syntheses of Doubly Locked Biliverdin Derivatives Toward Elucidation of the Stereochemistry of Phytochrome Chromophore.

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Synthesis of a Series of Mono-meso-arylmesoporphyrins III of Biological Interest and Their Biliverdin Derivatives

Synthesis of a series of mono-meso-arylmesoporphyrins III using a MacDonald-type 2+2 condensation is described. In this method, the substituted 1,9-diformyldipyrromethane is treated with a dipyrromethane-1,9-dicarboxylic acid under acidic conditions. The 5-aryldipyrrolic unit was obtained by condensation of tert-butyl, ethyl, or benzyl 4-ethyl-3-methyl-1H-pyrrole-2-carboxylate with different aromatic aldehydes in the presence of 4-toluenesulfonic acid. In order to obtain the corresponding mesobiliverdins, chemical oxidation of each mesoporphyrin was carried out. Each meso-arylmesoporphyrin rendered two isomeric arylbiliverdins, as the porphyrin meso-aryl bridge is not cleaved.

Total Syntheses of Doubly Locked Biliverdin Derivatives toward Elucidation of the Stereochemistry of Phytochrome Chromophore

Abstract To elucidate the stereochemistry of phytochrome chromophore in far-red light absorbing form (Pfr), four different types of doubly locked biliverdin (BV) derivatives, 5Zs15Ea-BV, 5Za15Ea-BV, 5Es15Ea-BV, and 5Ea15Ea-BV, were synthesized for the first time in free acid forms.

Syntheses of Biliverdin Derivatives Sterically Locked at the CD‐Ring Components.

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Syntheses of Biliverdin Derivatives Sterically Locked at the CD-Ring Components

Abstract Total syntheses of biliverdin derivatives with a Z-syn, Z-anti, or E-syn CD-ring components were accomplished via new and efficient methods for the construction of sterically locked CD-ring components towards the elucidation of the stereochemistry of the chromophore in phytochromes.

Sterically Locked Synthetic Bilin Derivatives and Phytochrome Agp1 from Agrobacterium tumefaciens Form Photoinsensitive Pr- and Pfr-like Adducts

Phytochrome photoreceptors undergo reversible photoconversion between the red-absorbing form, Pr, and the far-red-absorbing form, Pfr. The first step in the conversion from Pr to Pfr is a Z to E isomerization around the C15=C16 double bond of the bilin chromophore. We prepared four synthetic biliverdin (BV) derivatives in which rings C and D are sterically locked by cyclizing with an additional carbon chain. In these chromophores, which are termed 15Za, 15Zs, 15Ea, and 15Es, the C15=C16 double bond is in either the Z or E configuration and the C14-C15 single bond in either the syn or anti conformation. The chromophores were assembled with Agrobacterium phytochrome Agp1, which incorporates BV as natural chromophore. All locked BV derivatives bound covalently to the protein and formed adducts with characteristic spectral properties. The 15Za adduct was spectrally similar to the Pr form and the 15Ea adduct similar to the Pfr form of the BV adduct. Thus, the chromophore of Agp1 adopts a C15=C16 Z configuration and a C14-C15 anti conformation in the Pr form and a C15=C16 E configuration and a C14-C15 anti conformation in the Pfr form. Both the 15Zs and the 15Es adducts absorbed only in the blue region of the visible spectra. All chromophore adducts were analyzed by size exclusion chromatography and histidine kinase activity to probe for protein conformation. In either case, the 15Za adduct behaved like the Pr and the 15Ea adduct like the Pfr form of Agp1. Replacing the natural chromophore by a locked 15Ea derivative can thus bring phytochrome holoprotein in the Pfr form in darkness. In this way, physiological action of Pfr can be studied in vivo and separated from Pr/Pfr cycling and other light effects.

Synthesis of Biliverdin Derivative Bearing the Sterically Fixed E-anti C/D-Ring Component

Abstract Biliverdin (BV) derivative bearing the E-anti C/D-ring component, which is sterically fixed by 8-membered ring, was synthesized toward investigation of the structure and function of the chromophore in phytochrome.

Synthesis of the Sterically Fixed Biliverdin Derivative Bearing the Z‐anti C/D‐Ring Component.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of the Sterically Fixed Biliverdin Derivative Bearing the Z-anti C/D-Ring Component

Abstract A sterically locked biliverdin derivative was synthesized by developing an efficient method for the preparation of Z-anti C/D-ring component toward investigation of the stereochemistry and function of the phytochrome chromophores.

Quantum Mechanical Design of Molecular Computers Elements Suitable for Self-Assembling to Quantum Computing Living Systems

There are presented logic gates of molecular electronics digital computers. Maximal length of these molecular electronics digital logic gates are no more than four nanometers and maximal width 2.5 nm. The results of light induced internal molecular motions in azo-dyes molecules have been used for the design of light driven logically controlled (OR, AND) molecular machines composed from organic photoactive electron donor dithieno[3,2-b:2',3'-d]thiophene and ferrocene molecules, electron accepting tetracyano-indane molecule, and moving azo-benzene molecular fragment. Density functional theory (DFT) B3PW91/6-311G model calculations were performed for the geometry optimization of these molecular electronics logical gates. Applied DFT time dependent (DFT-TD/B3PW91) method and our visualization program give absorption spectra of designed molecular gates and show from which fragments electrons are hopping in various excited states. Quantum mechanical investigations of proton Nuclear Magnetic Resonance (NMR) values of Cu, Co, Zn, Mn and Fe biliverdin derivatives and their dimers using ab initio Hartree-Fock (HF) and DFT methods indicate that these modified derivatives should generate from one to twelve Quantum Bits (QuBits). The chemical shifts are obtained as the difference of the values of the tetramethylsilane (Si(CH3)4) molecule Gauge-Independent Atomic Orbital (GIAO) nuclear magnetic shielding tensor on the hydrogen atoms and that of the magnetically active molecules. There are designed several single supermolecule and supramolecular devices containing molecular electronics digital logic gates, photoactive molecular machines and elements of molecular NMR quantum computers that allowed to design several supramolecular Control NOT NMR quantum computing gates. Self-assembling simulations of these molecular quantum computing gates induced idea of self-assembled molecular quantum supercomputer and molecular quantum computing life.

Biliverdin Binds Covalently to Agrobacterium Phytochrome Agp1 via Its Ring A Vinyl Side Chain

The widely distributed phytochrome photoreceptors carry a bilin chromophore, which is covalently attached to the protein during a lyase reaction. In plant phytochromes, the natural chromophore is coupled by a thioether bond between its ring A ethylidene side chain and a conserved cysteine residue within the so-called GAF domain of the protein. Many bacterial phytochromes carry biliverdin as natural chromophore, which is coupled in a different manner to the protein. In phytochrome Agp1 of Agrobacterium tumefaciens, biliverdin is covalently attached to a cysteine residue close to the N terminus (position 20). By testing different natural and synthetic biliverdin derivatives, it was found that the ring A vinyl side chain is used for chromophore attachment. Only those bilins that have ring A vinyl side chain were covalently attached, whereas bilins with an ethylidene or ethyl side chain were bound in a noncovalent manner. Phycocyanobilin, which belongs to the latter group, was however covalently attached to a mutant in which a cysteine was introduced into the GAF domain of Agp1 (position 249). It is proposed that the regions around positions 20 and 249 are in close contact and contribute both to the chromophore pocket. In competition experiments it was found that phycocyanobilin and biliverdin bind with similar strength to the wild type protein. However, in the V249C mutant, phycocyanobilin bound much more strongly than biliverdin. This finding could explain why during phytochrome evolution in cyanobacteria, the chromophore-binding site swapped from the N terminus into the GAF domain.

Metallobiliverdin radicals--DFT studies.

Several aspects of the molecular and electronic structure of biliverdin derivatives have been studied using density functional theory (DFT). The calculations have been performed for complexes of trianion (BvO2)3- and dianion [BvO(OH)]2-, derived from two tautomeric forms of biliverdin, BvO2H3 and [BvO(OH)]H2, with redox innocent metal ions: lithium(I), zinc(II), and gallium(III). One-electron-oxidized and reduced forms of each complex (cation and anion radicals) have been also considered. The molecular structures of all species investigated are characterized by a helical arrangement of tetrapyrrolic ligands with the metal ion lying in the plane formed by the two central pyrrole rings. The spin density distribution in four types of metallobiliverdin radicals--[(BvO2.)Mn+]n-2,[[BvO(OH).]Mn+]n-1 (cation radicals),[(BvO2.)Mn+]n-4,[[BvO(OH).]Mn+]n-3 (anion radicals)--has been investigated. In general, the absolute values of spin density on meso carbon atoms were larger than for the beta-carbon atoms. Sign alteration of spin density has been found for meso positions, and also for the beta-carbon atoms of at least two pyrrole rings. The calculated spin density maps accounted for the essential NMR spectroscopic features of iron biliverdin derivatives, including the considerable isotropic shifts detected for the meso resonances and shift alteration at the meso and beta-positions.

Regioselective Porphyrin Bridge Cleavage Controlled by Electronic Effects. Coupled Oxidation of 3-Demethyl-3-(trifluoromethyl)mesohemin IX and Identification of Its Four Biliverdin Derivatives.

This report describes the nonenzymatic oxidative cleavage of the title porphyrin (2) performed with oxygen and ascorbic acid in aqueous pyridine at 37 degrees C (coupled oxidation), via hydrolysis of the corresponding verdoheme intermediates, followed by esterification of the resulting free acid mesobiliverdin analogues to their dimethyl esters 4 (alpha isomer), 5 (beta isomer), 6 (gamma isomer), and 7 (delta isomer). The four biliverdin derivatives were purified by HPLC, and their structures were confirmed by FAB MS and also by UV-vis and (1)H NMR spectroscopies. The purity of each compound was checked by (19)F NMR, and the four regioisomers were assigned through their 2D-NMR ROESY spectra and confirmed by UV-vis spectroscopy. The ratio of regioisomers was determined by (19)F NMR spectroscopy before any purification of single compounds was attempted: alpha:beta:gamma:delta 11:6:26:57 (%). This unusually high regioselectivity was attributed to the electron-withdrawing effect of the CF(3) group on the electronic structure of porphyrin as shown considering the ab initio calculations of an iron(II) beta-substituted (trifluoromethyl)porphyrin used as a model compound. In porphyrin 2, the oxidation clearly takes place at the electron richest meso positions, the order of reactivity strictly following that of electron density, pointing out that the regiospecificity of the bridge cleavage can be effectively controlled by the electronic effects of some strategic substituents in the chromophore. The relevance of all these results in the study of the mechanism of the reactions involved in the natural catabolism of heme, catalyzed by heme oxygenase, is discussed. The advantages of 2 derived from this work, which make it a suitable model compound for the enzymatic reaction, are also discussed.