There is an increasing demand for facile delivery of silyl groups onto organic bioactive molecules. One of the common methods of silylation via a transition-metal-catalyzed coupling reaction employs ...hydrosilane, disilane, and silylborane as major silicon sources. However, the labile nature of the reagents or harsh reaction conditions sometimes render them inadequate for the purpose. Thus, a more versatile alternative source of silyl groups has been desired. We hereby report a design, synthesis, and implementation of storable sodium silylsilanolates that can be used for the silylation of aryl halides and pseudohalides in the presence of a palladium catalyst. The developed method allows a late-stage functionalization of polyfunctionalized compounds with a variety of silyl groups. Mechanistic studies indicate that (1) a nucleophilic silanolate attacks a palladium center to afford a silylsilanolate-coordinated arylpalladium intermediate and (2) a polymeric cluster of silanolate species assists in the intramolecular migration of silyl groups, which would promote an efficient transmetalation.
Microcrystals of l‐Asn‐d‐Trp‐l‐Phe‐NH2 (NdWFamide), a tripeptide derived from Aplysia kurodai that exhibits invertebrate cardiac activity, were evaluated by vibrational circular dichroism (VCD). The ...chirality of the tryptophan residue at the second position in NdWFamide was associated with the conformation and biological characteristics. The VCD spectrum of NdWFamide was a mirror image of its enantiomer; however, it was significantly different from that of its diastereomer, NWFamide, which is its precursor. The obtained VCD signals of NdWFamide were in good agreement with the VCD signals that were calculated based on the optimized aggregates of NdWFamide, which formed a helical‐like backbone conformation. The evaluation of the VCD results revealed the conformation of NdWFamide in the crystalline state and succeeded in distinguishing its stereoisomers. Therefore, this study demonstrates VCD as a useful method for the structural analysis of naturally occurring d‐amino acid‐containing peptides.
The water chestnut Trapa bispinosa Roxb. has been domesticated in China and has been reported as the only domesticated species of this genus. To understand the origin of T. bispinosa and its ...evolution pathway, we compared the genetic similarity and seed morphology of domesticated water chestnut T. bispinosa with three wild species T. natans, T. incisa, and T. japonica along with archeological seed samples from the Tianluoshan site (approximately 7000–6300 cal BP) in China. The largest seed size was observed only in the domesticated species, whereas other wild species showed smaller size including T. natans L. genetically close to the domesticated type, and T. incisa was the smallest in size. The volumes of the seed capsule and endosperm were measured using X ray CT scans, showing the ratios of total volumes between T. bispinosa and wild species ranged from 4.2 to 4.5. The ratios of endosperm volume ranged from 3.3 to 3.7. Both measurements showed domesticated species have larger seed volume. Genome size was indirectly estimated by flow cytometry. Domesticated species with larger seed size was estimated as diploid, as were the wild species except for tetraploid species T. japonica. Domesticated species clearly showed the largest edible organs, but it was not a result of ploidy level changes. Maternal lineages traced using complete whole chloroplast sequences, suggested that T. natans is the closest to T. bispinosa, both of which are close to T. japonica. The result was confirmed by PCR genotyping with chloroplast insertion/deletion (cpINDEL) markers developed in the study. T. incisa showed distinct plastid types within the species, and T. japonica showed a unique plastid genotype. Our study concludes the largest volumes for the edible endosperm have been accomplished through nearly 6000 years of artificial selection, but the domestication did not involve ploidy level changes.
Evolutionary history of ploidy level was confirmed among wild and domesticated water chestnut. Complete chloroplast genome sequences were applied to know maternal origin of domesticated species.
Potamogeton ×angustifolius (P. gramineus × P. lucens) was newly recorded in Japan from a pond in Tsugaru-shi, Aomori Prefecture. The hybrid nothospecies was identified based on morphological ...observations and measurements, molecular analyses using cloned nuclear adhA gene and chloroplast rpl20–rps12 intergenic spacer, and pollen viability. The putative hybrid had morphological traits intermediate between P. gramineus and P. lucens, nuclear haplotypes matching those of the two parental lineages, and lower pollen viability than P. lucens (not compared with P. gramineus). The maternal lineage of the hybrid was presumed to be P. gramineus, based on chloroplast sequences. The hybrid characteristically shows well-branched stems in the upper part of shoots, as in P. gramineus, and both clearly petiolate and sessile submerged leaves with distinctive netted venation. Similar plants were collected in the 1980s from a ditch near the pond, suggesting that the hybrid may have been present for more than 30 years in this area.
Camphor continues to serve as a versatile chiral building block for chemical synthesis. We have developed a novel method to functionalize the camphor skeleton at C8 using an intramolecular hydrogen ...atom abstraction. The key advance involves the use of a camphor-derived aminonitrile, which is converted to the corresponding nitrogen-centered radical under photoredox conditions to effect the 1,5-hydrogen atom transfer at C8. The resulting carbon-centered radical at C8 was utilized in a C–H amination to access topologically complex proline derivatives. Furthermore, the total synthesis of several sesquiterpenoids was accomplished by engaging the radical generated at C8 in alkylation reactions.
A small semiartificial pond, revealing high species richness with respect to the aquatic macrophytes, was studied in the Aomori Prefecture, Japan. The pond had been completely formed ca. 10 years ...previously after excavation into a wet bog. To identify and evaluate its aquatic macrophyte flora during 2017–2018, we listed the species of aquatic vascular plants and charophytes in the pond and compared this list with those from the natural Japanese lakes using a database of aquatic flora in Japan. Two species were identified by molecular analyses because they lacked any reproductive organs, which were necessary for identifying the species level. We found a total of 57 taxa of aquatic macrophytes including 15 Red List species in Japan or Aomori Prefecture. Comparing the flora list with those from the 66 natural Japanese lakes surveyed since 2001, the pond was ranked fourth in the order of diversity (based on species richness) and rarity (based on numbers of Red List species). Therefore, the pond is an important aquatic environment in terms of aquatic macrophyte conservation in Japan. Interestingly, for a pond with such high species diversity, it is relatively small (0.14 km2), semiartificial, and relatively recently formed.
The multifaceted implementation of silanols in organic synthesis is reviewed from the standpoint of developments in transition metal-catalyzed reactions. The major properties of silanols are ...summarized according to the research fields that have utilized these intriguing species: silanols as nucleophiles to serve as bulky surrogates for water; silanols as temporary ligands to control regioselectivity of metal-catalyzed reactions; silanols as coupling partners for transferring functional groups. These topics are summarized to provide opportunities for future developments in the chemistry of silanols.
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