Biosynthesis of Indole Diterpene Lolitrems: Radical-Induced Cyclization of an Epoxyalcohol Affording a Characteristic Lolitremane Skeleton

Lolitrems are tremorgenic indole diterpenes that exhibit a unique 5/6 bicyclic system of the indole moiety. Although genetic analysis has indicated that the prenyltransferase LtmE and the cytochrome P450 LtmJ are involved in the construction of this unique structure, the detailed mechanism remains to be elucidated. Herein, we report the reconstitution of the biosynthetic pathway for lolitrems employing a recently established genome-editing technique for the expression host Aspergillus oryzae. Heterologous expression and bioconversion of the various intermediates revealed that LtmJ catalyzes multistep oxidation to furnish the lolitrem core. We also isolated the key reaction intermediate with an epoxyalcohol moiety. This observation allowed us to establish the mechanism of radical-induced cyclization, which was firmly supported by density functional theory calculations and a model experiment with a synthetic analogue.     

Metal-Free Twofold Electrochemical C−H Amination of Activated Arenes: Application to Medicinally Relevant Precursor Synthesis

The efficient production of many medicinally or synthetically important starting materials suffers from wasteful or toxic precursors for the synthesis. In particular, the aromatic non-protected primary amine function represents a versatile synthetic precursor, but its synthesis typically requires toxic oxidizing agents and transition metal catalysts. The twofold electrochemical amination of activated benzene derivatives via Zincke intermediates provides an alternative sustainable strategy for the formation of new C−N bonds of high synthetic value. As a proof of concept, we use our approach to generate a benzoxazinone scaffold that gained attention as a starting structure against castrate-resistant prostate cancer. Further improvement of the structure led to significantly increased cancer cell line toxicity. Thus, exploiting environmentally benign electrooxidation, we present a new versatile and powerful method based on direct C−H activation that is applicable for example the production of medicinally relevant compounds.     

Aromaticity and magnetotropicity of dicyclopenta-fused polyacenes

Most dicyclopenta-fused polyacenes are predicted to be moderately aromatic and diatropic, although they have no (4n + 2)-site conjugated circuits. We applied our graph theory of aromaticity and magnetotropicity to these molecules and found that these anomalous properties arise from a set of non-conjugated circuits, which contribute collectively to aromaticity and diatropicity. This result indicates that the conjugated circuit model is not always applicable to such non-alternant hydrocarbons. Dianions of dicyclopenta-fused polyacenes are more aromatic than their respective neutral species, because they are iso-pi-electronic with aromatic polyacenes.     

Macrocyclic conjugation pathways in porphyrins

Macrocyclic aromaticity is the most important concept in porphyrinoid chemistry. Bond resonance energy (BRE) for any pi-bond linking adjacent pyrrolic or other rings represents the stabilization energy due to macrocyclic aromaticity. We found that a main conjugation pathway associated with macrocyclic aromaticity can be traced by choosing a pi-bond with a larger BRE at every bifurcation of the pi-network. All pi-bonds located along the main conjugation pathway are intensified with large positive BREs compared with those located along the bypasses. On the other hand, a main destabilization pathway associated with macrocyclic antiaromaticity can be traced by choosing a pi-bond with a smaller BRE at every bifurcation of the pi-network. Macrocyclic conjugation pathways thus determined are fully consistent with the chemical shifts of protons attached to the macrocycle.     

Flash chemistry: fast chemical synthesis by using microreactors

This concept article provides a brief outline of the concept of flash chemistry for carrying out extremely fast reactions in organic synthesis by using microreactors. Generation of highly reactive species is one of the key elements of flash chemistry. Another important element of flash chemistry is the control of extremely fast reactions to obtain the desired products selectively. Fast reactions are usually highly exothermic, and heat removal is an important factor in controlling such reactions. Heat transfer occurs very rapidly in microreactors by virtue of a large surface area per unit volume, making precise temperature control possible. Fast reactions often involve highly unstable intermediates, which decompose very quickly, making reaction control difficult. The residence time can be greatly reduced in microreactors, and this feature is quite effective in controlling such reactions. For extremely fast reactions, kinetics often cannot be used because of the lack of homogeneity of the reaction environment when they are conducted in conventional reactors such as flasks. Fast mixing using micromixers solves such problems. The concept of flash chemistry has been successfully applied to various organic reactions including a) highly exothermic reactions that are difficult to control in conventional reactors, b) reactions in which a reactive intermediate easily decomposes in conventional reactors, c) reactions in which undesired byproducts are produced in the subsequent reactions in conventional reactors, and d) reactions whose products easily decompose in conventional reactors. The concept of flash chemistry can be also applied to polymer synthesis. Cationic polymerization can be conducted with an excellent level of molecular-weight control and molecular-weight distribution control.     

New nucleotide pairs for stable DNA triplexes stabilized by stacking interaction

New nucleotide pairs applicable to formation of DNA triplexes were developed. We designed oligonucleotides incorporating 5-aryl deoxycytidine derivatives (dC5Ars) and cyclic deoxycytidine derivatives, dCPPP and dCPPI, having an expanded aromatic area, as the second strand. As pairing partners, two types of abasic residues (C3: propylene linker, phi: abasic base) were chosen. It was concluded that, when the 5-aryl-modified cytosine bases paired with the abasic sites in TFOs in a space-fitting manner, the stability of the resulting triplexes significantly increased. The recognition of C3 toward dC5Ars was selective because of the stacking interactions between their aromatic part and the nucleobases flanking the abasic site. These results indicate the potential utility of new nucleotide triplets for DNA triplex formation, which might expand the variety of structures and sequences and might be useful for biorelated fields such as DNA nanotechnologies.     

Analysis of photo-induced hydration of a photochromic poly(N-isopropylacrylamide) - Spiropyran copolymer thin layer by quartz crystal microbalance

We investigated hydration and swelling behavior of a solid state photoresponsive copolymer in water by using a quartz crystal microbalance technique with dissipation measurement (QCM-D technique). On the gold film electrode of a quartz resonator, we deposited a thin layer of a pNSp-NIPAAm, which is a poly(N-isopropylacrylamide) (pNIPAAm) polymer partially modified with a photochromic chromophore, 6-nitrospiropyran (NSp). Using QCM-D measurements, we found that at a temperature of 19 °C both water adsorption and changes in the viscoelasticity of the solid pNSp-NIPAAm layer were induced when pNSp-NIPAAm was irradiated by 365 nm ultraviolet light, which triggers the photoisomerization of the NSp chromophore and makes the structure of the chromophore hydrophilic. At temperatures between 25 and 35 °C, this photo-induced hydration was not observed. These observations suggest that the photoisomerization of the NSp chromophores triggered the photo-induced hydration only when pNIPAAm component is sufficiently hydrophilic, at a temperature of 19 °C.     

Intrinsic carrier doping in antiferromagnetically interacted supramolecular copper complexes with (pyrazino)tetrathiafulvalene (pyra-TTF) as the ligand, [CuIICl2(pyra-TTF)] and (pyra-TTF)2[CuI3Cl4(pyra-TTF)

New supramolecular copper complexes with pyrazinotetrathiafulvalene (pyra-TTF) as the ligand, [Cu(II)Cl2(pyra-TTF)] (1) and (pyra-TTF) 2[Cu(I)3Cl4(pyra-TTF)] (2), have been synthesized by the diffusion method. Complex 1 is a black block crystal with a three-dimensional (3-D) supramolecular network; the linear chain [-Cu(II)Cl2-(pyra-TTF)-] n extends along the b axis, where the coordinated pyra-TTF donors are stacked in a head-to-tail and ring-over-bond configuration to construct two-dimensional (2-D) sheets, and between the sheets, there are C...Cl(-) or H...Cl(-) contacts. Even though the electron spin resonance (ESR) measurement reveals the nearly Cu(II) state, complex 1 is a semiconductor with sigmaRT=1.0 x 10(-4) S cm(-1) and Ea=0.33 eV. The high-frequency conductivity measurement also confirmed the intrinsic slight carrier doping from Cu(II) to the pyra-TTF donor. This slight doping enhances not only the real and imaginary dielectric constants but also the antiferromagnetic interaction between Cu(II) spins following the 2-D Heisenberg model with 2J=-20 K. In contrast, complex 2 is a very thin black needle. This needle crystal has two crystallographically independent pyra-TTF molecules, which are coordinated and noncoordinated donors. The coordinated donors composed a supramolecular chain [Cu(I)3Cl4(pyra-TTF)(0)]n , whereas the noncoordinated donors formed conducting alpha'-type pyra-TTF(+0.5) sheets. This complex is semiconducting with sigmaRT=0.1 S cm(-1) and Ea=0.15 eV. Both complexes 1 and 2 demonstrate that the pyra-TTF molecule works not only as an oxidized donor by Cu(II) to construct conducting sheets but also as a ligand coordinated to a Cu cation to form supramolecuar chains.     

Unique Thermal Structural Phase Transitions Exhibited by Unsymmetrical Organometallic Gold(III)-Dithiolene Complexes with Pentylthio and Hexylthio Groups

Unsymmetrical gold(III)-dithiolene complexes are potential candidates for molecular materials that exhibit thermal structural phase transitions. In this study, unsymmetrical ppy-gold(III) (ppy⁻=C-deprotonated-2-phenylpyridine(−)) complexes [AuC5] and [AuC6] coordinated by dithiolene ligands containing tetrathiafulvalene (TTF) skeletons with pentylthio (2-{bis(pentylthio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate(2−)) and hexylthio groups (2-{bis(hexylthio)-1,3-dithiol-2-ylidene}-1,3-dithiol-4,5-dithiolate(2−)) were synthesized. Both complexes exhibited a large absorption band at approximately 508 nm, owing to intramolecular ligand-to-ligand charge transfer. One-dimensional columnar structures with head-to-tail molecular arrangements around the metal ions were constructed in the crystals. The flexible alkylthio groups were intercalated into crystalline spaces between dithiolene ligands in the columns. [AuC5] exhibits a simple phase transition at 198 °C between crystalline and isotropic phases irreversibly. The crystalline phase of [AuC6] observed at 25 °C melted at 148 °C. Another crystalline phase grew above 148 °C with a very slow crystallization rate from the liquid phase and was completely transformed into an isotropic phase at 200 °C.