New open-chain tetrapyrroles as chromophores in the plant photoreceptor phytochrome

A series of six open-chain tetrapyrroles has been synthesized and used as chromophores for the plant photoreceptor protein phytochrome. The novel chromophores vary in the size of substituents 17 and 18 at ring D. This ring undergoes maximal conformational change upon light excitation ( Z --> E photoisomerization of the 15,16-double bond). Instead of methyl and vinyl substituents (positions 17, 18) as present in the native chromophore phytochromobilin, dimethyl, methyl and isopropyl, methyl and tert-butyl, ethyl and methyl, vinyl and methyl, and isopropyl and methyl substituents have been generated. All novel chromophores assemble with the apoprotein. The obtained chromoproteins show hypsochromic shifts of the absorbance maxima by 10 nm maximally, compared to the native pigment, except for the 17-isopropyl-18-methyl-substituted compound which showed a 100 nm hypsochromic shift of selectively the P r form. The assembly kinetics were slowed down in correlation to the increasing size of the substituents, with stronger effects for modified substituents at position 17. The thermal stability of the photoinduced P fr form for the 18-isopropyl and the 18- tert butyl substituents was even greater than that of the native pigments. Those chromophores carrying substituents at position 17 larger than the methyl group (ethyl and isopropyl) showed a very low stability of the respective P fr forms. Time-resolved detection of the P r to P fr conversion (laser-induced flash photolysis) revealed a slower formation of the P fr form for those chromophores carrying larger substituents at position 18, whereas the rise and decay kinetics of the early intermediates are only moderately changed. Introduction of larger substituents at position 17 (ethyl, vinyl, and isopropyl) causes drastic changes in the kinetics; in particular the formation of the first thermally stable intermediate, I 700, is significantly slowed, making a detection of its rise possible.     

Phytochromes with noncovalently bound chromophores: the ability of apophytochromes to direct tetrapyrrole photoisomerization

Chromophore-apoprotein interactions were studied with recombinant apoproteins, oat phytochrome (phyA) and CphB of the cyanobacterium Calothrix PCC7601, which were both incubated with the bilin compounds biliverdin (BV) IXalpha, phycocyanobilin (PCB) and the 3'-methoxy derivative of PCB. Previously it was shown that CphB and its homolog in Calothrix, CphA, show strong sequence similarities with each other and with the phytochromes of higher and lower plants, despite the fact that CphB carries a leucine instead of a cysteine at the chromophore attachment position and thus holds the chromophore only noncovalently. CphA binds tetrapyrrole chromophores in a covalent, phytochrome-like manner. For both eyanobacterial phytochromes, red and far-red light-induced photochemistry has been reported. Thus, the role of the binding site of CphB in directing the photochemistry of noncovalently bound tetrapyrroles was analyzed in comparison with the apoprotein from phyA phytochrome. Both the aforementioned compounds, which were used as chromophores, are not able to form covalent bonds with a phytochrome-type apoprotein because of their chemical structure (vinyl group at position 3 or methoxy group at position 3'). The BV adducts of both apoproteins showed phytochrome-like photochemistry (formation of red and far-red-absorbing forms of phytochrome [P(r) and P(fr) forms]). However, incubation of the oat apophytochrome with BV primarily yields a 700 nm form from which the P(r)-P(fr) photochemistry can be initiated and to which the system relaxes in the dark after illumination. The results for CphB were compared with a CphB mutant where the chromophore-binding cysteine had been introduced, which, upon incubation with PCB, shows spectral properties nearly identical with its (covalently binding) CphA homolog. A comparison of the spectral properties (P(r) and P(fr) forms) of all the PCB- and BV-containing chromoproteins reveals that the binding site of the cyanobacterial apoprotein is better suited than the plant (oat) phytochrome to noncovalently incorporate the chromophore and to regulate its photochemistry. Our findings support the proposal that the recently identified phytochrome-like prokaryotic photoreceptors, which do not contain a covalently bound chromophore, may trigger a light-induced physiological response.     

Preparation of pyrrole and pyrrolidine derivatives of pyrimidine. 1‐(2‐pyrimidinyl)pyrrole ‐ an inhibitor of X. phaseoli and X. malvacearum

Pyrrole and pyrrolidine derivatives of pyrimidine were prepared in which the nitrogen atom of the pyrrole or pyrrolidine ring is bonded directly to the 2‐ or 4‐carbon atom of the pyrimidine ring. Pyrrole derivatives were prepared by the dry distillation of an intimate mixture of an aminopyrimidine with mucic acid and by the reaction of a chloropyrimidine with potassium pyrrole. Pyrrolidine derivatives were prepared by the reaction of a chloropyrimidine with pyrrolidine and, in a single instance, by the catalytic hydrogenation of a pyrimidinylpyrrole. At a concentration of 200 mcg/mL, 1‐(2‐pyrimidinyl)pyrrole inhibited two plant pathogenic bacteria — Xanthomanus phaseoli (pathogenic on the bean plant) and Xanthomanus malvacearum (pathogenic on the cotton plant).     

Application of the Mössbauer spectroscopy to the study of the oxidation state of azaferrocene derivatives

Azaferrocene has two active sites of iron and nitrogen atoms. Drastic change of the oxidation state in iodine oxidation of azaferrocene is observed by introducing the methyl substituents into the pyrrole ring, while all the N-methylates show a similar electronic state. It was revealed that an introduction of methyl substituent to the pyrrole ring promotes the oxidation of nitrogen atom in pyrrole ring more than the central iron atom.     

Constructing sandwich-type rare Earth double-decker complexes with N-confused porphyrinato and phthalocyaninato ligands

Reaction of the half-sandwich complexes M(III)(Pc)(acac) (M = La, Eu, Y, Lu; Pc = phthalocyaninate; acac = acetylacetonate) with the metal-free N-confused 5,10,15,20-tetrakis[(4-tert-butyl)phenyl]porphyrin (H(2)NTBPP) or its N2-position methylated analogue H(CH(3))NTBPP in refluxing 1,2,4-trichlorobenzene (TCB) led to the isolation of M(III)(Pc)(HNTBPP) (M = La, Eu, Y, Lu) or Y(III)(Pc)[(CH(3))NTBPP] in 8-15% yield. These represent the first examples of sandwich-type rare earth complexes with N-confused porphyrinato ligands. The complexes were characterized with various spectroscopic methods and elemental analysis. The molecular structures of four of these double-decker complexes were also determined by single-crystal X-ray diffraction analysis. In each of these complexes, the metal center is octa-coordinated by four isoindole nitrogen atoms of the Pc ligand, three pyrrole nitrogen atoms, and the inverted pyrrole carbon atom of the HNTBPP or (CH(3))NTBPP ligand, forming a distorted coordination square antiprism. For Eu(III)(Pc)(HNTBPP), the two macrocyclic rings are further bound to a CH(3)OH molecule through two hydrogen bonds formed between the hydroxyl group of CH(3)OH and an aza nitrogen atom of the Pc ring or the inverted pyrrole nitrogen atom of the HNTBPP ring, respectively. The location of the acidic proton at the inverted pyrrole nitrogen atom (N2) of the protonated double-deckers was revealed by (1)H NMR spectroscopy.     

THEORETICAL STUDIES OF BILIPROTEIN CHROMOPHORES AND RELATED BILE PIGMENTS BY MOLECULAR ORBITAL AND RAMACHANDRAN TYPE CALCULATIONS

Abstract Ramachandran calculations have been used to gain insight into steric hindrance in bile pigments related to biliprotein chromophores. The high optical activity of denatured phycocyanin, as compared to phycoerythrin, has been related to the asymmetric substitution at ring A, which shifts the equilibrium towards the P-helical form of the chromophore. Geometric effects on the electronic structures and transitions have then been studied by molecular orbital calculations for several conjugation systems including the chromophores of phycocyanin, phytochrome P_r, cations, cation radicals and tautomeric forms. For these different chromophores some general trends can be deduced. For instance, for a given change in the gross shape (e.g. either unfolding of the molecule from a cyclic-helical to a fully extended geometry, or upon out-of-plane twists of the pyrrole ring A) of the molecules under study, the predicted absorption spectra all change in a similar way. Nonetheless, there are characteristic distinctions between the different n -systems, both in the transition energies and the charge distribution, which can be related to their known differences in spectroscopic properties and their reactivity.     

A Simple Preparation Method for Phytochromobilin

Phytochromobilin (PΦB), the chromophore of plant phytochromes, is difficult to isolate because phytochromes occur at very low concentrations in plants. It is, therefore, frequently replaced in plant phytochrome studies by phycocyanobilin, which is abundant in cyanobacteria. PΦB is also an attractive chromophore for far‐red emitting chromoproteins. In this work, we design and optimize a simple method to efficiently isolate useful quantities of PΦB: The chromophore is generated in Escherichia coli and transiently bound to a tailored chromophore‐binding domain of ApcE2, the apo‐protein of a core‐membrane linker, from which it can subsequently be released. The ease and effectiveness of this method hinges not only on the enhanced biosynthesis of PΦB in the presence of the ApcE2 construct from Synechococcus sp. PCC7335, but also on the noncovalent binding of the pigment to its apo‐protein. The isolated PΦB was successfully incorporated into phytochrome‐related assemblies, and furthermore, the noncovalently bound PΦB could be transferred directly from the ApcE2 construct to the apo‐proteins of phytochromes, cyanobacteriochromes and phycobiliproteins, without loss of relevant biological activity.     

Significant impact of deprotonated status on the photoisomerization dynamics of bacteriophytochrome chromophore

We report that the photoinduced dynamics of the phytochrome chromophore is strongly dependent on the protonation/deprotonation states of the pyrrole ring. The on-the-fly surface hopping dynamics simulations were performed to study the photoisomerization of different protonation/deprotonation phytochrome chromophore models. The simulation results indicate that the deprotonations at the pyrrole rings significantly modify the photoinduced nonadiabatic dynamics, leading to distinctive population decay dynamics and different reaction channels. Such feature can be well explained by the formation of the different hydrogen bond network patterns. Therefore, the proper understanding of the photoisomerization mechanism of phytochrome chromophore must take the hydrogen bond network into account. This work provides the new insights into the photobiological functions of phytochrome chromophore and suggests the possible ideas to control of its photoconversion processes for further rational engineering in optical applications.     

含氮给体结构对丙烯腈电荷转移光聚合的影响

<正> 对于正性烯类单体,主要是乙烯基咔唑的电荷转移聚合,诚田已作过详细综述。负性烯类单体的电荷转移聚合主要研究的单体是丙烯腈(AN)及甲基丙烯酸甲酯(MMA)。Barton等研究了芳烃为引发剂的MMA光聚合。我们研究了芳胺为引发剂的光聚合。 芳胺,尤其是芳叔胺,是较强的电子给体,与负性单体在光照下经激基复合物而引发聚合,我们的实验表明,吡啶及其同系物(喹啉与吖啶)并不象吡咯及其同系物(吲哚与咔唑)那样有效地引发AN等负性单体的光聚合(见表1)。从图1所示的结构看,它们有     

A remarkable skeletal rearrangement of a coordinated tetrapyrrole: chemical consequences of palladium pi-coordination to a bilindione.

Pd4(OEB)2, in which a [Pd2]2+ unit is bound in pi-fashion to olefinic sites that are exocyclic to pyrrole rings of the octaethylbilindione ligand, undergoes an unprecedented sequence of reactions that results in the rearrangement of the framework of the bilindione ligand and the formation of trans-Pd(py)2I2. This process of bilindione rearrangement and oxidation occurs as a direct consequence of the pi-coordination of the palladium. The reaction results in the migration of a nitrogen atom from a pyrrole carbon atom to what was formerly a meso carbon atom to transform a former pyrrole ring into a six-membered ring. This process also involves cleavage of the Pd-Pd and Pd-C bonds, oxidation of palladium, and introduction of an oxygen atom (from water) not necessarily in this particular sequence.     

Heteronuclear NMR investigation on the structure and dynamics of the chromophore binding pocket of the cyanobacterial phytochrome Cph1

Structural changes of the chromophore in phytochrome proteins associated with its photocycle are still not fully understood. We use heteronuclear NMR to investigate the conformation and dynamics of the chromophore in the binding pocket of the cyanobacterial phytochrome Cph1. On the basis of distance information obtained from three-dimensional nuclear Overhauser enhancement (3D-NOESY) spectra using the photochemically intact photosensory module of Cph1 we demonstrate that the chromophore is in the ZZZssa form in the P(r) (red absorbing form) state and the ZZEssa form in the P(fr) (far-red absorbing form) state of the protein. While ZZZssa for the P(r) state is in agreement with a recently determined X-ray structure, no comparable information for the P(fr) state of photochemically intact phytochrome has been available up to now. In addition, the chromophore in the binding pocket of Cph1 exhibits a notable mobility, which is distinctly different in the two photostates.     

Synthesis and matrix metalloproteinase-12 inhibitory activity of ageladine A analogs

Synthesis of the 37 ageladine A analogs was accomplished by employing the total synthetic route of natural ageladine A previously explored by us. From the matrix metalloproteinase-12 (MMP-12) inhibitory activity assay carried out using the novel analogs, it appeared evident that the halogen atom at the 2-position of pyrrole ring was essential for the inhibitory activity and that the introduction of a bromine atom into the 4-position of pyrrole ring is very effective for producing potent activity. In addition, exchange of the pyrrole ring to an imidazole ring was extremely effective in increasing activity, and the analog 29 thus obtained was found to show approximately 4 times more potent activity than natural ageladine A.     

Electronic structure and electron transport characteristics of a cobalt complex

The molecular and electronic structures and electron transport characteristics of a Co complex are investigated using first principles calculations. The Co complex belongs to the D(2d) point group, and its two ligands are perpendicular to each other. The central atom Co forms a distorted octahedron with six donor N atoms. In a low oxidation state, the bond length between Co and pyrrole nitrogen, 1.849 A, is much shorter than the distance between Co and pyridine nitrogen, 2.168 A, while, in a high oxidation state, the bond length differences between Co and pyrrole nitrogen, 1.814 A, and between Co and pyridine nitrogen, 1.990 A, are not as large as those in the Co2+ complex. The HOMO energy of the low oxidation state is very close to the Fermi level of bulk Au, allowing hole creation in the molecule. On the other hand, the LUMO energy of the high oxidation state is close to the Au Fermi level, allowing a low barrier for electron injection from the Au cathode to the molecule. These structural characteristics make the Co complex a good hole-conduction molecule. The density of states, transmission probability, and I-V characteristics are evaluated using the Green function approach.     

Derivatives of octahydropyrrolo[4,3,2-m,n]-acridine. 5. Alkylation of 1-methyl and 1-aryl-4,4,8,8-tetramethyl-2,3,4,5,7,8,9,10-octahydropyrrolo[4,3,2-m,n]acridin-10-ones

4,4,8,8-Tetramethyl-2,3,4,5,7,8,9,10-octahydropyrrolo[4,3,2-m,n]acridin-10-ones were alkylated at the nitrogen atom of the pyrrole ring by successive treatment with sodium hydride and an alkyl halide. Treatment of the neutral molecule with methyl iodide gave alkylation at the nitrogen atom of the pyridine ring. Derivatives of pyrrolo[4,3,2-m,n]acridine with no substituent at position 2 readily lost a proton from the NH group of the pyrrole ring to give bipolar structures.For Communication 2, see [1]; for Communications 3 and 4, see [2, 3].Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 794–802, June, 1998.     

N-substituted 2,5-Di(2-thienyl)pyrroles. Synthesis and electrochemical properties

2,5-Dithienylpyrroles containing p-substituted benzene ring at the nitrogen atom were synthesized. The formylation and subsequent crotonic condensation of N-(4-nitrophenyl)-2,5-di (2-thienyl)pyrrole was performed. Electrochemical behavior of the compounds and electrochromic properties of 2,5-di(2-thienyl)-pyrrole containing p-semidine fragment at its nitrogen atom were studied.     

Phosphorylation of N‐iso‐propyl‐ and N‐tert‐butylpyrroles with phosphorus(III) halides

The investigation concerns the effect of a bulky substituent at the pyrrole nitrogen atom on the orientation and regioselectivity of pyrrole phosphorylation with phosphorus(III) halides. As shown, phosphorylation of N‐iso‐propylpyrrole with phosphorus tribromide or trichloride proceeds nonregioselectively at positions 2 and 3 but it is followed by the 2 → 3 migration of the dihalogenophosphine group which quantitatively yields the 3‐isomer. N‐tert‐butylpyrrole is regioselectively phosphorylated with halogenophosphines at position 3. The tert‐butyl substituent at the nitrogen atom does not preclude the binding of even two or three pyrrolyl residues to the phosphorus atom. The key compounds, 3‐pyrrolyldihalogenophosphines, were isolated in a pure state, characterized and used to obtain a number of stable phosphorus(V) derivatives. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:599–604, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20158     

Indachlorins: Nonplanar Indanone‐Annulated Chlorin Analogues with Panchromatic Absorption Spectra between 300 and 900 nm

Indaphyrins, pyrrole‐modified porphyrins containing a cleaved pyrrole β,β′‐bond and two annulated indanone moieties, possess unusually broadened and redshifted UV/Vis spectra because of their π‐expanded chromophores. The parent free base indaphyrin has been crystallographically characterized, highlighting its strongly ruffled conformation incorporating a helimeric twist. It was shown to be susceptible to regiospecific derivatizations at the opposite side of the ring‐cleaved pyrrole (dihydroxylation, followed by functional group transformations of the resulting diol functionality), generating indaphyrin‐based chlorin analogues, indachlorins, that incorporate a dihydroxypyrroline, pyrrolindione, oxazolone, or a morpholine moiety. Structural modifications resulted in further broadening and hyper‐ and bathochromic shifts of the optical spectra, some of which possess a nearly panchromatic absorption between 300 to well above 900 nm. The extents to which these modifications affect their solid‐state conformations were analyzed.     

THE MODE OF INTERACTION BETWEEN BLUE (UV) LIGHT PHOTORECEPTOR AND PHYTOCHROME IN ANTHOCYANIN FORMATION OF THE SORGHUM SEEDLING

Two non-photosynthetic photoreceptors (phytochrome and a blue light photoreceptor) are involved in light-mediated anthocyanin synthesis in the mesocotyl of Sorghum seedlings. The present study was undertaken to investigate the kind of interaction between phytochrome and the blue light photoreceptor. The data show that phytochrome (P_fr) can only act once a blue light effect has occurred. On the other hand, the blue light effect cannot express itself without P_fr. It is concluded that there is an obligatory dependency (or sequential interaction) between the blue light effect and the light effect occurring through phytochrome, although the blue light photoreaction per se is not affected by the presence or absence of phytochrome. The latter statement is based on the results of dichromatic experiments, i.e. simultaneous, high fluence rate irradiation with two kinds of light. Blue light can be replaced by UV light. It is not clarified yet whether the effect of blue and UV light is due to the same photoreceptor.     

A 3D QSAR pharmacophore model and quantum chemical structure--activity analysis of chloroquine(CQ)-resistance reversal

Using CATALYST, a three-dimensional QSAR pharmacophore model for chloroquine(CQ)-resistance reversal was developed from a training set of 17 compounds. These included imipramine (1), desipramine (2), and 15 of their analogues (3-17), some of which fully reversed CQ-resistance, while others were without effect. The generated pharmacophore model indicates that two aromatic hydrophobic interaction sites on the tricyclic ring and a hydrogen bond acceptor (lipid) site at the side chain, preferably on a nitrogen atom, are necessary for potent activity. Stereoelectronic properties calculated by using AM1 semiempirical calculations were consistent with the model, particularly the electrostatic potential profiles characterized by a localized negative potential region by the side chain nitrogen atom and a large region covering the aromatic ring. The calculated data further revealed that aminoalkyl substitution at the N5-position of the heterocycle and a secondary or tertiary aliphatic aminoalkyl nitrogen atom with a two or three carbon bridge to the heteroaromatic nitrogen (N5) are required for potent "resistance reversal activity". Lowest energy conformers for 1-17 were determined and optimized to afford stereoelectronic properties such as molecular orbital energies, electrostatic potentials, atomic charges, proton affinities, octanol-water partition coefficients (log P), and structural parameters. For 1-17, fairly good correlation exists between resistance reversal activity and intrinsic basicity of the nitrogen atom at the tricyclic ring system, frontier orbital energies, and lipophilicity. Significantly, nine out of 11 of a group of structurally diverse CQ-resistance reversal agents mapped very well on the 3D QSAR pharmacophore model.     

Primary reactions of bacteriophytochrome observed with ultrafast mid-infrared spectroscopy

Phytochromes are red-light photoreceptor proteins that regulate a variety of responses and cellular processes in plants, bacteria, and fungi. The phytochrome light activation mechanism involves isomerization around the C(15)═C(16) double bond of an open-chain tetrapyrrole chromophore, resulting in a flip of its D-ring. In an important recent development, bacteriophytochrome (Bph) has been engineered for use as a fluorescent marker in mammalian tissues. Bphs covalently bind a biliverdin (BV) chromophore, naturally abundant in mammalian cells. Here, we report an ultrafast time-resolved mid-infrared spectroscopic study on the Pr state of two highly related Bphs from Rps. palustris , RpBphP2 (P2) and RpBphP3 (P3) with distinct photoconversion and fluorescence properties. We observed that the BV excited state of P2 decays in 58 ps, while the BV excited state of P3 decays in 362 ps. By combining ultrafast mid-IR spectroscopy with FTIR spectroscopy on P2 and P3 wild type and mutant proteins, we demonstrate that the hydrogen bond strength at the ring D carbonyl of the BV chromophore is significantly stronger in P3 as compared to P2. This result is consistent with the X-ray structures of Bph, which indicate one hydrogen bond from a conserved histidine to the BV ring D carbonyl for classical bacteriophytochromes such as P2, and one or two additional hydrogen bonds from a serine and a lysine side chain to the BV ring D carbonyl for P3. We conclude that the hydrogen-bond strength at BV ring D is a key determinant of excited-state lifetime and fluorescence quantum yield. Excited-state decay is followed by the formation of a primary intermediate that does not decay on the nanosecond time scale of the experiment, which shows a narrow absorption band at ～1540 cm(-1). Possible origins of this product band are discussed. This work may aid in rational structure- and mechanism-based conversion of BPh into an efficient near-IR fluorescent marker.