Concerning the Diastereomerization of Stilbenoid Hypericin Derivatives

Summary.  Experiments on a newly prepared (E)-configured ω-benzal-hypericin derivative using TLC and ¹H NMR together with quantum chemical calculations revealed that in stilbenoid hypericin derivatives photodiastereomerization between the (E)- and (Z)-diastereomers occurs in principle. However, due to its low diastereomerization quantum yield and photo and thermal equilibria, which reside mostly on the side of the (E)-diastereomer, this photoreaction is only of marginal importance to the photochemistry of stilbenoid hypericin derivatives. Thus, photodiastereomerization does not appreciably interfere with the photoreactions important for photodynamic therapy. This was demonstrated by comparing the sensitized bilirubin photodestruction of hypericin and the ω-benzal-hypericin derivative. Received December 6, 2001. Accepted December 21, 2001     

Concerning the Absorption and Photochemical Properties of an ω-4-Dimethylaminobenzal Hypericin Derivative

Summary.  A hypericin derivative containing ω,ω ′-4-dimethylaminobenzal residues was shown to undergo an intramolecular [2 + 2] cycloaddition upon irradiation leading to a cyclobutane derivative whose main absorption band is hardly shifted as compared to hypericin. The corresponding ω-substituted derivative displayed a 34 nm bathochromic shift and a strongly reduced fluorescence quantum yield rendering it a nice candidate for a photodynamic therapy agent. Unfortunately, however, it produced virtually no photosensitized active oxygen species, making it thus unsuited for this purpose. Received July 11, 2001. Accepted July 18, 2001     

Synthesis and Properties of 10,11-Dibenz-imidazolyl-10,11-didesmethyl-hypericin – The First Heterocyclically Substituted Hypericin Derivative

Summary. The synthesis of the first heterocyclically substituted title hypericin derivative was achieved starting from 6-benzimidazolyl-tri-O-methyl-6-desmethylemodin. The chemical as well as photochemical properties of this unique hypericin derivative, which might constitute a new photodynamic therapy agent, are reported.     

Toward hypericin-derived potential photodynamic therapy agents

To optimize a hypericin derivative as a potential photodynamic therapy agent its light-induced singlet oxygen/superoxide radical formation capability should be enhanced and its long-wavelength absorption band should be bathochromically shifted to better match medicinal lasers. A heavy-atom-substituted derivative was realized by electrophilic iodination of hypericin to yield 2,5-diiodo-hypericin. Using photodestruction of bilirubin IX alpha this derivative was demonstrated to exhibit an enhanced light-induced singlet oxygen/superoxide radical formation capability as compared to hypericin. With respect to a bathochromically shifted derivative styryl residues were attached to the methyl groups of hypericin by de novo ring synthesis. Although the long-wavelength absorption band of this derivative displayed a bathochromic shift of nearly 40 nm it unfortunately immediately underwent an intramolecular [2 + 2] cycloaddition to yield the corresponding cyclobutane derivative in which the added conjugation system became interrupted.     

A Route to Amino Functionalized Hypericin Derivatives and their Chemical and Photochemical Properties Pertaining to Photodynamic Therapy

Summary. Syntheses of amino functionalized hypericin derivatives could be achieved starting from the recently prepared emodin derived 1,3,8-trimethoxy-6-amino-9,10-anthraquinone. Our strategies for the preparation of 10,11-didemethyl-10,11-diaminohypericin, 10,11-didemethyl-10,11-di(acetylamino) hypericin, and its hypericinoidic diazepine derivative include synthetical modifications on the levels of the anthraquinone, anthron, and the phenanthroperylenequinone system itself. The chemical as well as photochemical properties of these unique hypericin derivatives, which might constitute new photodynamic therapy agents, are reported.     

ω,ω′-Appended nucleo-base derivatives of hypericin

ω,ω′-Disubstituted hypericin derivatives with the nucleo-bases thymine, cytosine, and adenine in these positions were prepared starting from tri-O-methyl-ω-bromoemodin. The most promising derivative proved to be that with a thymine moiety. It displayed the best solubility of the three products together with a potency to produce singlet oxygen and/or reactive oxygen species comparable to the parent compound hypericin. In addition, although no specific interaction with DNA or poly(2′-deoxyadenylic acid) could be detected, it proved to be significantly better accumulating in the nucleus of prostatic cancer LNCaP cells than hypericin making it a promising candidate for a second-generation photodynamic hypericin agent.     

ω,ω′-Urea- and -dithioacetal-derivatives of hypericin

An ω,ω′-disubstituted hypericin derivative bearing two dicyclohexylurea moieties separated by propionyl chains from the chromophore and an ω,ω′-dithioacetal of hypericin were prepared. Both showed excellent production of oxidizing species comparable to hypericin when irradiated with appropriate light as shown by the photodestruction of bilirubin IXα.     

On synthesis and properties of hypericin-porphyrin hybrids

Two diastereomeric tetraphenylporphyrinyl-ω-hypericinyl-ethylenes were prepared and their properties investigated. The (Z)-diastereomer displayed an even higher photosensitization of singlet oxygen and/or reactive oxygen species than hypericin, whereas the (E)-configured derivative showed a somewhat weaker effect. Accordingly, hybridization of hypericin and porphyrin chromophores seems to be a promising target for the development of novel sensitizers for photodynamic therapy. Correspondence: Heinz Falk, Department of Organic Chemistry, Johannes Kepler University Linz, 4040 Linz, Austria, Europe.     

Concerning the Diastereomerization of Stilbenoid Hypericin Derivatives

 Experiments on a newly prepared (E)-configured ω-benzal-hypericin derivative using TLC and ¹H NMR together with quantum chemical calculations revealed that in stilbenoid hypericin derivatives photodiastereomerization between the (E)- and (Z)-diastereomers occurs in principle. However, due to its low diastereomerization quantum yield and photo and thermal equilibria, which reside mostly on the side of the (E)-diastereomer, this photoreaction is only of marginal importance to the photochemistry of stilbenoid hypericin derivatives. Thus, photodiastereomerization does not appreciably interfere with the photoreactions important for photodynamic therapy. This was demonstrated by comparing the sensitized bilirubin photodestruction of hypericin and the ω-benzal-hypericin derivative.     

ω,ω′-Urea- and -dithioacetal-derivatives of hypericin

An ω,ω′-disubstituted hypericin derivative bearing two dicyclohexylurea moieties separated by propionyl chains from the chromophore and an ω,ω′-dithioacetal of hypericin were prepared. Both showed excellent production of oxidizing species comparable to hypericin when irradiated with appropriate light as shown by the photodestruction of bilirubin IXα.     

Synthesis and Properties of 10,11-Dibenz-imidazolyl-10,11-didesmethyl-hypericin – The First Heterocyclically Substituted Hypericin Derivative

The synthesis of the first heterocyclically substituted title hypericin derivative was achieved starting from 6-benzimidazolyl-tri-O-methyl-6-desmethylemodin. The chemical as well as photochemical properties of this unique hypericin derivative, which might constitute a new photodynamic therapy agent, are reported.     

1H NMR determination of hypericin and pseudohypericin in complex natural mixtures by the use of strongly deshielded OH groups

The ¹H NMR spectra of the commercially available compounds hypericin and its derivative pseudohypericin in CD₃OH solutions indicate significantly deshielded signals in the region of 14-15 ppm. These resonances are attributed to the peri hydroxyl protons OH(6), OH(8) and OH(1), OH(13) of hypericins which participate in a strong six-membered ring intramolecular hydrogen bond with CO(7) and CO(14), respectively, and therefore, they are strongly deshielded. In the present work, we demonstrate that one-dimensional ¹H NMR spectra of hypericin and pseudohypericin, in Hypericum perforatum extracts show important differences in the chemical shifts of the hydroxyl groups with excellent resolution in the region of 14-15 ppm. The facile identification and quantification of hypericin and its derivative compound pseudohypericin was achieved, without prior HPLC separation, for two H. perforatum extracts from Greek cultivars and two commercial extracts: a dietary supplement, and an antidepressant medicine. The results were compared with those obtained from UV-vis and LC/MS measurements.     

A Route to Amino Functionalized Hypericin Derivatives and their Chemical and Photochemical Properties Pertaining to Photodynamic Therapy

Syntheses of amino functionalized hypericin derivatives could be achieved starting from the recently prepared emodin derived 1,3,8-trimethoxy-6-amino-9,10-anthraquinone. Our strategies for the preparation of 10,11-didemethyl-10,11-diaminohypericin, 10,11-didemethyl-10,11-di(acetylamino) hypericin, and its hypericinoidic diazepine derivative include synthetical modifications on the levels of the anthraquinone, anthron, and the phenanthroperylenequinone system itself. The chemical as well as photochemical properties of these unique hypericin derivatives, which might constitute new photodynamic therapy agents, are reported.     

ω,ω′-Appended nucleo-base derivatives of hypericin

ω,ω′-Disubstituted hypericin derivatives with the nucleo-bases thymine, cytosine, and adenine in these positions were prepared starting from tri-O-methyl-ω-bromoemodin. The most promising derivative proved to be that with a thymine moiety. It displayed the best solubility of the three products together with a potency to produce singlet oxygen and/or reactive oxygen species comparable to the parent compound hypericin. In addition, although no specific interaction with DNA or poly(2′-deoxyadenylic acid) could be detected, it proved to be significantly better accumulating in the nucleus of prostatic cancer LNCaP cells than hypericin making it a promising candidate for a second-generation photodynamic hypericin agent.     

Concerning the Absorption and Photochemical Properties of an ω-4-Dimethylaminobenzal Hypericin Derivative

 A hypericin derivative containing ω,ω ′-4-dimethylaminobenzal residues was shown to undergo an intramolecular [2 + 2] cycloaddition upon irradiation leading to a cyclobutane derivative whose main absorption band is hardly shifted as compared to hypericin. The corresponding ω-substituted derivative displayed a 34 nm bathochromic shift and a strongly reduced fluorescence quantum yield rendering it a nice candidate for a photodynamic therapy agent. Unfortunately, however, it produced virtually no photosensitized active oxygen species, making it thus unsuited for this purpose.     

The Protonation and Deprotonation Equilibria of Hypericin Revisited

Summary.  The protonation and deprotonation behaviour and the assignment of pK _a values of hypericin are reviewed and discussed. Three experiments (electrospray MS, ¹H NMR, acid–base indicator equilibria) provided additional evidences for the assignment of pK _a values of −5 and −6 to mono- and diprotonation at the carbonyl groups of hypericin, of pK _a = 2 to monodeprotonation at the bay-region, and of pK _a = 11 to dideprotonation at the bay- and peri-regions. Received September 26, 2001. Accepted October 1, 2001     

Cationic Hypericin Derivatives as Novel Agents with Photobactericidal Activity: Synthesis and Photodynamic Inactivation of Propionibacterium acnes

The present communication describes for the first time the synthesis and preliminary testing of two cationic hypericin derivatives. Uncharged hypericin derivatives with ω , ω '-attached C₂-linkers leading to a pyridyl or a 4-dimethylaminophenyl residue were prepared and subsequently quaternized by means of iodomethane. Photobactericidal activity was assessed using Propionibacterium acnes . The quaternary N , N , N -trimethyl-anilinium derivative displayed a pronounced photodynamic inactivation of the bacteria at low incubation concentrations (<100 n m ) and a short incubation time (1 h) after illumination with yellow light (590 nm, 20 J cm⁻²), whereas the photobactericidal efficacy of the N -methyl-pyridinium derivative was negligible under identical experimental conditions.     

Syntheses and Properties of Two Heterocyclically Substituted Hypericin Derivatives: 10,11-Dibenzothiazolyl-10,11-didemethylhypericin and 10,11-Dibenzoxazolyl-10,11-didemethylhypericin

Summary. The syntheses of the two heterocyclically substituted title hypericin derivatives were achieved starting either from 6-benzothiazolyl-tri-O-methyl-6-demethylemodin or 6-benzoxazolyl-tri-O-methyl-6-demethylemodin. The use of microwave assisted synthesis for the preparation of these anthraquinone synthons and the chemical as well as photochemical properties of the corresponding unique hypericin derivatives, which might constitute new photodynamic therapy agents, are reported. The tautomeric and stereochemical aspects of these hypericin derivatives were investigated by means of semiempirical calculations (AM1).     

Syntheses,Photochemical Properties,and Tautomerism of Intramolecularly <Emphasis Type="Italic">Friedel-Crafts</Emphasis> Acylated Hypericin Derivatives

Summary. Intramolecularly Friedel-Crafts acylation carried out on the hypericin moiety provided a new class of 9,12-dicarbonyl substituted hypericin derivatives as potential candidates for photodynamic therapy (PDT). Focusing on cyclopentanone and cyclohexanone condensed derivatives, investigations concerning the chemical and photochemical properties as well as the tautomerism of these compounds were performed.     

Determination of Hypericin in Hypericum perforatum (St. John’s Wort) Using Classical C18 and Pentafluorophenyl Stationary Phases: Contribution of Pi–Pi Interactions to High-Performance Liquid Chromatography (HPLC)

Hypericin is one of the most important bioactive substances present in Hypericum perforatum (Saint John’s Wort), which exhibits various biological activities such as inhibition of neuronal processes coupled with transmission of serotonin, dopamine, gamma-amino butyric acid and L-glutamine. This red-colored derivative of anthraquinone contains six benzene cycles and four hydroxy groups that polarize electron density in the conjugated double bond system and enable the molecule to act as a Lewis base in charge-transfer complexes. In this study, four stationary phases modified by the pentafluorophenyl group were selected to investigate the contribution of π-π interactions to the improvement of hypericin separation in comparison to the separation provided with a classical C18 based chromatographic column. In order to develop a suitable gradient chromatographic method for the quantification of hypericin, normal, polar organic and reverse elution modes were evaluated using high-performance liquid chromatography with ultraviolet-visible and mass spectrometry detection. It was disclosed in the analyses that the pentafluorophenyl stationary phase can separate hypericin from hyperforin, which was not possible to achieve with the C18 based stationary phase. The best analytical method found, employing the pentafluorophenyl stationary phase, showed sufficient linearity, accuracy and precision and was used for the determination of hypericin in Saint John’s Wort.