The synthesis and chiral resolution of free-base and Ni(II) complexes of a number of derivatives of meso-tetraphenylmorpholinochlorins, with and without direct β-carbon-to-o-phenyl linkages to the flanking phenyl groups, is described. The morpholinochlorins, a class of stable chlorin analogues, were synthesized in two to three steps from meso-tetraphenylporphyrin. The conformations and the relative stereostructures of a variety of free-base and Ni(II) complexes of these morpholinochlorins were elucidated by X-ray diffractometry. Steric and stereoelectronic arguments explain the relative stereoarray of the morpholino-substituents, which differ in the free-base and Ni(II) complexes, and in the monoalkoxy, β-carbon-to-o-phenyl linked morpholinochlorins, and the dialkoxy derivatives. The Ni(II) complexes were all found to be severely ruffled whereas the free-base chromophores are more planar. As a result of the helimeric distortion of their porphyrinoid chromophores, the ruffled macrocycles possess a stable inherent element of chirality. Most significantly, resolution of the racemic mixtures was achieved, both by classical methods via diastereomers and by HPLC on a chiral phase. Full CD spectra were recorded and modeled using quantum-chemical computational methods, permitting, for the first time, an assignment of the absolute configurations of the chromophores. The report expands the range of known pyrrole-modified porphyrins. Beyond this, it introduces large chiral porphyrinoid π-systems that exist in the form of two enantiomeric, stereochemically stable helimers that can be resolved. This forms the basis for possible future applications, for example, in molecular-recognition systems or in materials with chiroptic properties.

In this paper, the synthesis of a new type of intrinsically chiral, directly beta,beta'-linked, octa-meso-aryl-substituted bisporphyrins is described, by using an optimized Suzuki-Miyaura coupling procedure. This strategy leads to a broad variety of such axially chiral 'superbiaryls', differing in their metalation states and substitution patterns. On the basis of an efficient route to as-yet-unknown beta-boronic acid esters of various meso-tetraarylporphyrins (TAPs) by a two-step bromination-borylation protocol, 18 axially chiral bisporphyrin derivatives were prepared in good to excellent yields. As compared to all other directly linked dimeric porphyrin systems, the joint presence of eight bulky meso substituents and the peripheral position of the porphyrin-porphyrin linkage is unprecedented. The axial configurations and rotational barriers of the pure atropo-enantiomers were investigated by HPLC-CD experiments on a chiral phase in combination with quantum chemical CD calculations. According to the HPLC experiments and in agreement with quantum chemical calculations by applying the dispersion-corrected BLYP method, the configurational stability of the central porphyrin-porphyrin axis strongly depends on the nature of the central metals. Cyclovoltammetric studies proved the systematic influence of the meso substituents and of the metal ions on the oxidation potentials of the bisporphyrins. The novel axially chiral bis(tetrapyrrole) compounds described here are potentially useful as substrates for asymmetric catalysis, biomimetic studies on directed electron-transfer processes, for photodynamic therapy (PDT), and for chiral recognition.

We report on a comprehensive transient absorption study with β,β'-linked bis[tetraphenylporphyrinato-zinc(II)] and its corresponding monomer, covering the ultrafast dynamics from femtoseconds up to several microseconds. By exciting these porphyrins either to their first (S(1)) or second (S(2)) electronically excited states and by probing the subsequent dynamics, a multitude of reaction pathways have been identified. In the spectral region associated with the ground-state recovery of the bisporphyrin, transient absorption changes occur within the first few picoseconds, which are ascribable to excitonic interaction both in the S(2) (fs time-domain) and in the S(1) (ps time-domain) state. This is substantiated by complementary experiments with the monomeric porphyrin, in which the S(2) state exhibits a longer lifetime. In contrast to the picosecond dynamics the bisporphyrin and the monomer behave similarly on the nanosecond time-scale, that is nearly all excited molecules eventually reach a long-lived triplet excited state.

[reaction: see text] A novel type of "superbiaryl", the first porphyrin dimers with an intrinsically chiral structure, has been prepared. The atropo-enantiomers were configurationally assigned by HPLC-CD combined with quantum chemical CD calculations.

Chloropupukeanolides C-E (8-10), three highly functionalized secondary metabolites featuring a novel spiroketal skeleton derived from the chlorinated tricyclo-[4.3.1.0(3, 7)]-decane (pupukeanane) and the 2,6-dihydroxy-4-methylbenzoic acid moieties, were isolated from the scale-up fermentation extract of the plant endophytic fungus Pestalotiopsis fici. The constitutions of compounds 8-10 were elucidated primarily by NMR experiments. Their relative configurations were deduced by analogy to metabolites 4-6, which were previously isolated from the same fungus. The absolute configuration of 8 was assigned by X-ray crystallography and those of 9 and 10 by quantum-chemical CD calculations. Biogenetically, chloropupukeanolides C-E (8-10) are presumably derived from the same oxidation-induced Diels-Alder reaction pathway as compounds 1 and 4-7, via the putative biosynthetic precursors 2 and 3. The opposite configurations of the complete "Southern parts" of 8 and 9 suggests that this Diels-Alder reaction is stereochemically not very selective. Compounds 8-10 showed significant cytotoxicity against a small panel of human tumor cell lines and weak activities against the pathogens of tropical diseases.

Caught in the act: Genetic pathway engineering in conjunction with HPLC–NMR spectroscopy of highly labile intermediates provided direct evidence for the installation of β,γ double bonds during polyketide elongation to form the antibiotic bacillaene. The novel congener bacillaene B (1) was also discovered as an elusive true end product of the pathway in Bacillus amyloliquefaciens.

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Auf frischer Tat ertappt: Das Engineering genetischer Reaktionspfade zusammen mit der HPLC/NMR‐spektroskopischen Untersuchung sehr labiler Intermediate lieferte direkte Belege für den Aufbau von β,γ‐Doppelbindungen während der Polyketidverlängerung zum Antibiotikum Bacillaen. Des Weiteren wurde das neuartige Kongener Bacillaen B (1) als schwierig nachzuweisendes wahres Endprodukt des Pfades in Bacillus amyloliquefaciens entdeckt.