Cation-Stacking Approach Enabling Interconversion between Bis(xanthylium) and its Reduced Species.

Cyclophane-type dications with two units of xanthylium were designed, with the expectation that intramolecular interaction between cation units could induce changes in absorption and redox behavior. The desired dications were synthesized via the macrocyclic diketone as a key intermediate, which was efficiently obtained by a stepwise etherification. X-ray and UV/Vis measurements revealed that the cyclophane-type dications adopt a stacking structure in both the crystal and solution. Due to the intramolecular interaction caused by π-π stacking of the xanthylium units, a considerable blue shift compared to the corresponding monocations and a two-stage one-electron reduction process were observed in the dications. Furthermore, upon electrochemical reduction of dications, the formation of biradicals via radical cation species was demonstrated by UV/Vis spectroscopy with several isosbestic points at both stages. Therefore, the cation-stacking approach is a promising way to provide novel properties due to perturbation of their molecular orbitals and to stabilize the reduced species even though they have open-shell characters.

Class of cyclic ribosomal peptide synthetic genes in filamentous fungi.

Ustiloxins were found recently to be the first example of cyclic peptidyl secondary metabolites that are ribosomally synthesized in filamentous fungi. In this work, two function-unknown genes (ustYa/ustYb) in the gene cluster for ustiloxins from Aspergillus flavus were found experimentally to be involved in cyclization of the peptide. Their homologous genes are observed mainly in filamentous fungi and mushrooms. They have two "HXXHC" motifs that might form active sites. Computational genome analyses showed that these genes are frequently located near candidate genes for ribosomal peptide precursors, which have signal peptides at the N-termini and repeated sequences with core peptides for the cyclic portions, in the genomes of filamentous fungi, particularly Aspergilli, as observed in the ustiloxin gene cluster. Based on the combination of the ustYa/ustYb homologous genes and the nearby ribosomal peptide precursor candidate genes, 94 ribosomal peptide precursor candidates that were identified computationally from Aspergilli genome sequences were classified into more than 40 types including a wide variety of core peptide sequences. A set of the predicted ribosomal peptide biosynthetic genes was experimentally verified to synthesize a new cyclic peptide compound, designated as asperipin-2a, which comprises the amino acid sequence in the corresponding precursor gene, distinct from the ustiloxin precursors.

Characterization of the biosynthetic gene cluster for the ribosomally synthesized cyclic peptide ustiloxin B in Aspergillus flavus.

Ustiloxin B is a secondary metabolite known to be produced by Ustilaginoidea virens. In our previous paper, we observed the production of this compound by Aspergillus flavus, and identified two A. flavus genes responsible for ustiloxin B biosynthesis (Umemura et al., 2013). The compound is a cyclic tetrapeptide of Tyr-Ala-Ile-Gly, whose tyrosine is modified with a non-protein coding amino acid, norvaline. Although its chemical structure strongly suggested that ustiloxin B is biosynthesized by a non-ribosomal peptide synthetase, in the present study, we observed its synthesis through a ribosomal peptide synthetic (RiPS) pathway by precise sequence analyses after experimental validation of the cluster. The cluster possessed a gene (AFLA_094980), termed ustA, whose translated product, UstA, contains a 16-fold repeated peptide embedding a tetrapeptide, Tyr-Ala-Ile-Gly, that is converted into the cyclic moiety of ustiloxin B. This result strongly suggests that ustiloxin B is biosynthesized through a RiPS pathway and that UstA provides the precursor peptide of the compound. The present work is the first characterization of RiPS in Ascomycetes and the entire RiPS gene cluster in fungi. Based on the sequence analyses, we also proposed a biosynthetic mechanism involving the entire gene cluster. Our finding indicates the possibility that a number of unidentified RiPSs exist in Ascomycetes as the biosynthetic genes of secondary metabolites, and that the feature of a highly repeated peptide sequence in UstA will greatly contribute to the discovery of additional RiPS.

Bis(triarylmethylium)-type Macrocyclic Dications: Mechanochromic Emission Extending to the Red Region.

Macrocyclic dications 22+ composed of two triarylmethylium units were designed and synthesized. In contrast to the reference monocations 1+ , macrocyclic dications 22+ exhibited mechanochromic emission extending to the red region (-900 nm), since the luminescence color in a solid state can reversibly change due to their constrained structures granted by alkylene linkers and the choice of a proper counterion. X-ray diffraction and spectroscopic analyses revealed that such mechanochromic behavior was induced by the crystal-to-amorphous transition. A change in the intermolecular interaction of macrocyclic dications 22+ would be the key to realizing a change in the emission pattern, since the color of the molecules did not change by applying mechanical stimuli. These findings may suggest a design strategy for creating a variety of stimuli-responsive materials, especially for carbocation-based fluorescent materials.

Genetic patterning in the adult capitate antenna of the beetle Tribolium castaneum.

Antenna structure varies widely among insects, in contrast to the well-conserved structure of legs. The adult capitate antenna of the red flour beetle, Tribolium castaneum, is composed of eleven articles, organized into four distinct morphological regions (scape, pedicel, funicle and club). Here, we report the use of RNA interference to examine the functions of 21 genes during antenna metamorphosis in T. castaneum. Genes with conserved functions relative to the developmental model species Drosophila melanogaster include Distal-less and EGF signaling (antennal growth), spineless (determination of antennal identity) and the Notch signaling pathway (antennal growth, joint formation, and sensory bristle development). However, the functions of many genes differed from those predicted from the Drosophila model. In addition to a conserved gap phenotype, depletion of dachshund transformed funicle articles toward club-like identity. Depletion of Distal-less or homothorax did not cause antenna-to-leg transformation. Lim1 was required only for development of the scape-pedicle joint. Depletion of odd-skipped-related genes led to the loss of the entire funicle, while spalt, rotund, spineless, and dachshund affected smaller regions. Growth and joint formation were linked developmentally in the funicle, but not in the club. Joint formation within the club required bric-a-brac, aristaless, apterous, and pdm. Gene functions are discussed in terms of a model of antenna development in T. castaneum. This model provides a contrast to knowledge of antenna development in D. melanogaster, insight into the likely ancestral mode of antenna development, and a framework for considering diverse antenna morphologies.

Patterning of the adult mandibulate mouthparts in the red flour beetle, Tribolium castaneum.

Specialized insect mouthparts, such as those of Drosophila, are derived from an ancestral mandibulate state, but little is known about the developmental genetics of mandibulate mouthparts. Here, we study the metamorphic patterning of mandibulate mouthparts of the beetle Tribolium castaneum, using RNA interference to deplete the expression of 13 genes involved in mouthpart patterning. These data were used to test three hypotheses related to mouthpart development and evolution. First, we tested the prediction that maxillary and labial palps are patterned using conserved components of the leg-patterning network. This hypothesis was strongly supported: depletion of Distal-less and dachshund led to distal and intermediate deletions of these structures while depletion of homothorax led to homeotic transformation of the proximal maxilla and labium, joint formation required the action of Notch signaling components and odd-skipped paralogs, and distal growth and patterning required epidermal growth factor (EGF) signaling. Additionally, depletion of abrupt or pdm/nubbin caused fusions of palp segments. Second, we tested hypotheses for how adult endites, the inner branches of the maxillary and labial appendages, are formed at metamorphosis. Our data reveal that Distal-less, Notch signaling components, and odd-skipped paralogs, but not dachshund, are required for metamorphosis of the maxillary endites. Endite development thus requires components of the limb proximal-distal axis patterning and joint segmentation networks. Finally, adult mandible development is considered in light of the gnathobasic hypothesis. Interestingly, while EGF activity is required for distal, but not proximal, patterning of other appendages, it is required for normal metamorphic growth of the mandibles.