Breakdown of Chlorophyll: Partial synthesis of a putative intermediary catabolite. Preliminary communication

The partial synthesis of 10,22-dihydro-4,5-dioxo-4,5-secopheophorbide a ( 1 ) from pheophorbide a methyl ester (2) is described. A regioselective, photooxygenolytic reaction of (pheophorbidato a methyl ester)cadmium(II)( 3 ) provides the entry to the crucial 4,5-secoporphinoid structure in form of the (10,22-dihydro-4,5-dioxo-4,5-seco-pheophorbidato a methyl ester)cadmium(II) ( 4 ). The hydride reduction of this 4,5-dioxo-4,5-secophytoporphyrin ester occurs selectively at the ‘eastern’ meso-position to lead (after demetallation) to 10,22-dihydro-4,5-dioxo-4,5-secopheophorbide a methyl ester ( 5 ). This oxobilin-carbaldehyde has the structure assigned earlier to an ester of an isolation form of the red pigment(s) from Chlorella protothecoides. Hydrolysis of the propanoate ester function of 5, selectively catalyzed by pig liver esterase, then yields the title compound 1 . The red tetrapyrrole 1 may represent an intermediary chlorophyll catabolite in degreening plants.     

CHLOROPHYLL CATABOLISM. PART 3. STRUCTURE ELUCIDATION AND PARTIAL SYNTHESIS OF A NEW RED BILIN DERIVATIVE FROM Chlorella protothecoides*

The structure of a new red pigment produced during the “bleaching” of Chlorella protorhecoides cells has been elucidated by analytical methods as well as by in vitro isomerization into the new compound of a synthetic sample of a previously characteriLed chlorophyll a catabolite.     

Marine sponge melanin: a new source of an old biopolymer

Various types of melanin have already been found in the majority of organisms, being this biopolymer considered as one of the major pigments present in nature. The presence of this pigment in marine sponges (Phylum Porifera, one of the simplest multicellular organisms) was postulated, but never characterized. In this context this work aims the extraction and characterization of a dark pigment observed in four different marine sponges species (Erylus mamillaris, Erylus discophorus var. deficiens, Pachymatisma johnstonia, Dercitus bucklandi). Characterization of the extracted biopolymer was performed using solid state analytical techniques, due to the characteristic non-solubility of melanin. Therefore, characterization techniques like SEM–EDS, IR, UV–vis, MALDI-MS, elemental analysis and X-ray powder diffraction (XRD) were used to identify the biopolymer. The results showed that the extracted material was obtained with high purity, being identified as melanin. The results also emphasize a large structure variability present in this pigment, showing different structure arrangements and composition depending on its source, which influences the UV behaviour. The structural characterization of this class of pigments is fundamental, allowing a better understanding of melanin properties.     

STUDIES ON THE RED AND BLUE FORMS OF THE PIGMENT OF BLEPHARISMA*

Abstract— –The intracellular pigment of the ciliate protozoan Blepharisma in the presence of oxygen sensitizes the cells to bright visible light (2700 foot candles (fc)). Illumination of the cells with dim visible light (200 fc) changes the color of the pigment to blue-gray; such cells are no longer sensitive to bright visible light. The pigment which exists in granules can be extruded by cold treatment and is slowly regenerated. The suspension of red cells, the extruded pigment from them and an ethanol extract of the pigment all have very similar absorption spectra. Illumination of the red pigment in ethanol converts it to the blue form of the pigment but only if oxygen is present, indicating a photooxidation. The pigment can be oxidized in darkness to the blue form by ozonation. A suspension of blue cells, the extruded pigment from them and an ethanol extract from them, all have similar absorption spectra. The pigments in red and blue form are very similar spectrophotometrically and in solubility in three species of Blepharisma studies: B. americanum, B. intermedium and B. japonicum. The purified pigment has strong absorption in the far (200–300 nm) ultraviolet (u.v.) and may serve as a screen against damaging U.V. radiation, especially as Blepharisma shows poor photoreactivation.     

Macrocyclic Spermine Alkaloids from Verbascum: The (E/Z)-Isomeric Pairs (−)-(S)-Verbasitrine/(−)-(S)-Isoverbasitrine and (+)-(S)-Verbametrine/(+)-(S)-Isoverbametrine: Isolation,Structure Elucidation,and Synthesis

The isolation and structure elucidation of the 17-membered macrocyclic spermine alkaloids (−)-(S)-verbasitrine ( 2 ), (−)-(S)-isoverbasitrine ( 4 ), (+)-(S)-verbametrine ( 6 ), and (+)-(S)-isoverbametrine ( 8 ) is presented. The synthesis of their racemates is described.     

New Spirostaphylotrichins from the Mutant Strain P 649 of Staphylotrichum coccosporum: The Biogenetic Interrelationship of the Known Spirostaphylotrichins

The isolation and structure elucidation of the new Spirostaphylotrichins N ( 2 ), O ( 3 ), P ( 4 ), and T ( 7 ) from a mutant strain of S. coccosporum are described. The biogenetic relationship of the known spirostaphylotrichins is discussed.     

EBC-232 and 323: A Structural Conundrum Necessitating Unification of Five In Silico Prediction and Elucidation Methods

Structurally unique halimanes EBC-232 and EBC-323, isolated from the Australian rainforest plant Croton insularis, proved considerably difficult to elucidate. The two diastereomers, which consist an unusual oxo-6,7-spiro ring system fused to a dihydrofuran, were solved by unification and consultation of five in silico NMR elucidation and prediction methods [i.e., ACDLabs, olefin strain energy (OSE), DP4, DU8+ and TD DFT CD]. Structure elucidation challenges of this nature are prime test case examples for empowering future AI learning in structure elucidation.     

Macrocyclic Spermine Alkaloids from Verbascum: Isolation,Structure Elucidation,and Syntheses of the (E/Z)-Isomeric Pairs (S)-Verbasikrine/(S)-Isoverbasikrine and (S)-Verbamekrine/(S)-Isoverbamekrine

The isolation and structure elucidation of the 17-membered macrocyclic spermine alkaloids (S)-verbasikrine ( 3 ), (S)-isoverbasikrine ( 6 ), (S)-verbamekrine ( 9 ), and (S)-isoverbamekrine ( 12 ) is presented. The syntheses of their racemates are described. The HPLC/APCI-MS analysis of the original total alkaloid extract of Verbascum pseudonobile is presented.     

FIBER-OPTIC PLANT TISSUES: SPECTRAL DEPENDENCE IN DARK-GROWN AND GREEN TISSUES*

Abstract— The fiber-optic properties of etiolated plant tissues can be used to detect and characterize pigment absorption in vivo. Transmission spectra of light guided through several monocot and dicot etiolated tissues show a decreasing red/far red ratio with increasing tissue length. Absorption bands attributable both to vacuolar pigments such as anthocyanins and to chloroplast pigments lead to the conclusion that the guided light passes through both vacuole and cytoplasm. As etiolated tissue becomes green under white light treatment, the red/far red ratio also changes, the nature of the change depending upon the tissue involved. The blue/red ratio also changes both with increasing length of etiolated tissue and during the greening process, with the changes again dependent on the tissue involved. The spectral dependence of the light-guiding phenomenon in dark grown and green plants may have implications for physiological responses mediated by phytochrome.     

Synthesis of 2‐amino‐4h‐thiazolo[5,4‐b]indole and characterization of its colored conversion products with protein tyrosine phosphatase inhibitory activity

In DMSO‐solution 2‐amino‐4H‐thiazolo[5,4‐b]indole is converted into a complex mixture of colored products. The three major conversion end‐products, of which two are inhibitors of protein tyrosine phos‐phatases (PTPs), were isolated by chromatographic methods and their structures characterized by spectro‐scopic analysis, including NMR and MS combined with computer assisted structure elucidation, and, finally, confirmed by independent chemical synthesis. Synthesis of 2‐amino‐4H‐thiazolo[5,4‐b]indole as well as its N‐acetyl derivatives prepared from either oxindole or 2‐bromo‐1‐(2‐nitro‐phenyl)ethanone is described.     

Synthesis and evaluation of a new water-soluble fluorescent red dye,xanthene bis-C-glycoside

Condensation of 2 eq. of C-β-D-glucosylphloroacetophenone with glyoxylic acid in an aqueous solution of Na₂CO₃, followed by air oxidation in MeOH in the presence of 11 eq. of pyridine to afford a 36% yield of a bright red dye, xanthene bis-C-glycoside. This dye is 10 times more fluorescent (Φ_{f [EtOH]}^{581 nm} = 3.9 × 10⁻²) and 7.5 times more water-soluble (57 mg/mL H₂O) than the natural red pigment, carthamin. Detailed NMR analysis of its methyl analogs was used to confirm the structure of the dye as methyl 4,5-diacetyl-1,3,8-trihydroxy-3-oxo-3H-2,7-di-C-β-D-glucopyranosylxanthene-9-carboxylate from among three possible ring-closure isomers. Xanthene is safe and shows high light-resistance; therefore, xanthene bis-C-glycoside could be used as a food colorant or an in vivo probe.     

Pteridines. Part C. Structure and nonenzymatic synthesis of aurodrosopterin

The nonenzymatic synthesis of aurodrosopterin ( 5 ) from 6-acetyl-2-amino-3, 7, 8, 9-tetrahydro-4H-pyrimido-[4,5-b][1,4]diazepin-4-one ( 3 ) and 7,8-dihydrolumazine ( 4 ) at pH 3 (HCl) was performed. The identity of the synthesized compound with the natural eye pigment isolated from drosophila heads was confirmed by thin-layer chromatography on cellulose and by comparisons of the ¹H-NMR and UV/VIS spectra. The nonenzymatic synthesis of a neodrosopterin-like red pigment from 3 and 2,4-diamino-7,8-dihydropteridine was also carried out, but its identity could not be established. This pigment, called aminodrosopterin, has an absorption peak at 489 nm, which is very close to that of neodrosopterin.     

Novel Mechanism of Bioluminescence: Oxidative Decarboxylation of a Moiety Adjacent to the Light Emitter of Fridericia Luciferin

A novel luciferin from a bioluminescent Siberian earthworm Fridericia heliota was recently described. In this study, the Fridericia oxyluciferin was isolated and its structure elucidated. The results provide insight into a novel bioluminescence mechanism in nature. Oxidative decarboxylation of a lysine fragment of the luciferin supplies energy for light generation, while a fluorescent CompX moiety remains intact and serves as the light emitter.     

PHOTORECEPTOR PIGMENT IN Blepharisma: H+ RELEASE FROM RED PIGMENT

In faded cells of Blepharisma kept in a standard saline solution containing bacteria which had been cultured on agar plates containing glucose and polypepton, threshold light intensity for step-up photophobic response elevated. This result suggests that red pigment (blepharismin) contained in Blepharisma cells is involved in the step-up photophobic response. The pH of the aqueous solution of the red pigment was found to decrease when light was applied, indicating that the pigment releases H⁺ in response to light stimulation. However, faded pigment preparation by light irradiation did not show pH decrease. In the living cells faded by light irradiation, threshold light intensity for the step-up photophobic response was raised. Results suggest that H⁺ release from the red pigment induced by light irradiation might be responsible for the step-up photophobic response of the cells.     

IRRADIATION-ENHANCED PHYTOCHROME PELLETABILITY IN AVENA: PIGMENT RELEASE BY Mg2+-GRADIENT ELUTION

Abstract— Gradient elution is used to facilitate controlled withdrawal of Mg²⁺ from phytochrome-rich particulate fractions from irradiated Avena sativa L. shoots. The bound pigment from red-irradiated tissue is released in a discrete band when the Mg²⁺ falls to just below 1 mM. This phytochrome has an apparent molecular weight of ?300 kilodaltons upon gel filtration, indistinguishable from that of the unbound pigment in the same extract and from that in the 50,000 × g supernatant from non-irradiated Avena. This indicates that the bound phytochrome is released as a soluble molecule at a Mg²⁺ concentration above that which permits release of the particulate binding partner from other particulate components. These findings appear to preclude the possibility that the phytochrome-binding partner association can be selectively preserved at a Mg²⁺ level that would permit separation and analysis of phytochrome-bearing particles without the complication of Mg²⁺-induced membrane and RNP aggregation. “Cycled” P_fr (that from tissue irradiated with a red-far red sequence prior to homogenization) is released at 0.1 to 0.2 mM Mg²⁺. This indicates that “cycled P_r is more tenaciously bound by the particulate fraction than is P_fr. This effect is photoreversible both by further in vivo and subsequent in vitro irradiations, suggesting that the state of the pigment, rather than of the binding partner, directly controls the tenacity of the interaction. Increasing concentrations of KCl release the pigment from the particulate fraction in the presence of 10 mM Mg²⁺; increasing Triton X100 concentrations do not. This confirms the ionic nature of the pigment-particulate fraction interaction and indicates strongly that the phytochrome is located external to any membrane vesicles present (although not necessarily that it is bound directly to such vesicles). The data further suggest that phospholipid polar head groups are not primarily responsible for the binding.     

Laetiporic acid, a new polyene pigment from the wood-rotting basidiomycete Laetiporus sulphureus (Polyporales, Fungi)

A new pigment, laetiporic acid, has been isolated from fruit-bodies of the wood-rotting fungus Laetiporus sulphureus (sulfur shelf). Structure elucidation by application of extensive 2D NMR techniques permitted its identification as a polyene of non-isoprenoid origin. Laetiporic acid, which represents the main pigment in L. sulphureus basidiocarps, bears an unprecedented decaene skeleton as part of its chromophore and, interestingly, contains double bonds with a stable cis configuration.     

Studies on phosphonic acid antibiotics. I. Structure and synthesis of 3-(n-acetyl-n-hydroxyamino)propylphosphonic acid (FR-900098) and its n-formyl analogue (FR-31564)

The structure elucidation of FR-900098 ($\text{1}$) isolated from a microorganism source and the syntheses of FR-900098 and its N-formyl analogue, FR-31564 ($\text{2}$), are described. The latter possesses a superior antimicrobial activity.     

Quadricyclanes. Part I: Photoelectron spectra and electronic structure

The photoelectron spectra of quadricyclane ( 3 ) and 3-methylidene quadricyclane ( 4 ) have been measured. The results served as a basis for the elucidation of the electronic structure of these compounds, which agreed with theoretical calculations. It is found that the symmetry of the HOMO of 3 is different when compared to that of its valence isomer norbornadiene ( 1 ). The results also indicate that the structure of the highest occupied orbitals cannot be derived by only considering the Walsh-orbitals of the two three-membered rings. In addition one of the Walsh-components of the four-memebered ring has to be taken into account.     

Structure and Stereochemistry of New Sesquiterpene Esters from Echinacea purpurea (L.) MOENCH. (Preliminary communication)

The structure elucidation of four new constituents from the roots of Echinacea purpurea is described. They are shown to be cinnamoyl esters of sesquiterpene alcohols with a germacrane or a guaiane skeleton. First pharmacological results indicate immunological activities.     

Probing the Motional Behavior of Eumelanin and Pheomelanin with Solid‐State NMR Spectroscopy: New Insights into the Pigment Properties

Melanin is the most widespread pigment in the animal kingdom. Despite its importance, its detailed structure and overall molecular architecture remain elusive. Both eumelanin (black) and pheomelanin (red) occur in the human body. These two melanin compounds show very different responses to UV‐radiation exposure, which could relate to their microscopic features. Herein, the structural properties and motional behavior of natural eu‐ and pheomelanin extracted from black and red human hair are investigated by means of solid‐state NMR spectroscopy. Several 1D and 2D NMR spectroscopic techniques were combined to highlight the differences between the two forms of the pigment. The quantitative analysis of the ¹H NMR wide‐line spectra extracted from 2D ¹H–¹³C LG‐WISE experiments revealed the presence of two dynamically distinguishable components in both forms. Remarkably, the more mobile fraction of the pigment showed a higher mobility with respect to the proteinaceous components that coexist in the melanosome, which is particularly evident for the red pigment. An explanation of the observed effects takes into account the different architecture of the proteinaceous matrix that constitutes the physical substrate onto which melanin polymerizes within the eu‐ and pheomelanosomes. Further insight into the molecular structure of the more mobile fraction of pheomelanin was also obtained by means of the analysis of 2D ¹H–¹³C INEPT experiments. Our view is that not only structural features inherent in the pure pigment, but also the role of the matrix structure in defining the overall melanin supramolecular arrangement and the resulting dynamic behavior of the two melanin compounds should be taken into account to explain their functions. The reported results could pave a new way toward the explanation of the molecular origin of the differences in the photoprotection activity displayed by black and red melanin pigments.