Asymmetric total syntheses of (+)-mycoepoxydiene and related natural product (-)-1893A: application of one-pot ring-opening/cross/ring-closing metathesis to construct their 9-oxabicyclo[4.2.1]nona-2,4-diene skeleton

The total syntheses of (+)-mycoepoxydiene and (-)-1893A have been completed. The present synthetic strategy features the use of one-pot ring-opening/cross metathesis (ROM/CM) followed by a ring-closing metathesis (RCM) reaction, allowing for the concise construction of the 9-oxabicyclo[4.2.1]nona-2,4-diene framework from a 7-oxabicyclo[2.2.1]hept-2-ene derivative and 1,3-butadiene. The sequential metathesis product was converted into (+)-mycoepoxydiene through the oxidative rearrangement of a furfuryl alcohol to a pyranone, thereby establishing its absolute stereochemistry. From the common intermediate, a structurally related natural product (-)-1893A was also synthesized via the vinylogous aldol reaction.     

Synthesis and reactivities of 10-S-3 trithiadiazapentalene derivatives

1,3-Bis(p-substituted-phenylthiocarbamoyl)-2-imidazolidinethiones 3a-f reacted with bromine to give trithiadiazapentalene derivatives 5a-f , bearing the exocyclic C-N double bonds, in moderate yields. The molecular structure of 5b was elucidated by the X-ray crystallographic analysis. The treatment of 5b-f with hydrochloric acid gave the ring-opening products, 1,3-bis(p-substituted-phenylthiocarbamoyl)-2-imidazo-lidinones 9b-f , accompanied by the production of elemental sulfur. Reduction of 5b , 5d , and 5e with sodium borohydride gave the ring-opening compounds, 1,3-bis(p-substituted-phenylthiocarbamoyl)-2-imidazolidines 13b , 13d , and 13e respectively.     

Thermal stability of phthalate esters: Effect of substituents on the β-carbon atom

In order to clarify the mechanism conferring heat resistance on phthalate esters, those with a substituent on the β-carbon atom, such as bis(2-aminobutyl) phthalate, bis(2-nitrobutyl) phthalate, bis(2,4-diphenylbutyl) phthalate and dineopentyl phthalate, were synthesized and their thermal stabilities were studied by thermogravimetry and differential thermal analysis. The analytical results for these phthalate esters were compared with those for dibutyl phthalate, with a straight alkyl chain. As the temperatures required for a 3% weight loss of phthalate esters with a substituent, an electron-donating group (amino group) or an electron-accepting group (nitro group) on the β-carbon atom move to the higher end of the range, the effect of the adjacent group was recognized. The presence of a phenyl group in phthalate esters considerably improved the heat resistance. It is considered that the high heat resistance of bis(2,4-diphenylbutyl) phthalate is due to the obstruction of the planar configuration for cis elimination by the phenyl group and hindrance by the phenyl group of the formation of the six-membered cyclic transition state owing to the interaction between non-bondable molecules.     

7,10,14-Tri-t-butyl-3-amino-1,8-bisdehydro[14]annulene

Tri-t-butylcarboxybisdehydro[14]annulene was converted by the Curtius reaction into unstable aminoannulene, which could be characterized as N-acetyl derivative. The pK_a-value of the aminoannulene reflects aromatic nature of the annulene nucleus.     

Localization of Iα and Iβ phases in algal cellulose revealed by acid treatments

Highly crystalline I-rich type Cladophora cellulose, which had been kept in never-dried condition, was treated in 60wt% sulfuric acid at 100°C, for 1–48h. The cellulose microcrystals thus obtained were analysed by X-ray diffractometry, FT-IR, and transmission electron microscopy. The I component was found to be more degraded than the I component. The cellulose I/I ratios of the samples acid-treated for 0, 24, and 48 h were about 8:2, 6:4, and 4:6, respectively. After the acid treatment, the microcrystals became narrower in width, and very sharp at their ends. These results indicate that the I phase is mostly located at the surface of the microcrystals, which is morphologically more susceptible to the acid treatment.     

Studies on diacetylenic vinyl compounds. VI. ESR studies on the polymerization of diacetylene containing acrylate and methacrylates

A number of diacetylene containing acrylate and methacrylates have been synthesized and the interaction between their propagating radicals and the diacetylene groups was studied by ESR spectroscopy. In the case of polymerization at 70°C using AIBN as an initiator, the propagating radicals of methacrylates are temporarily trapped with the diacetylenes with rapid exchange of the electron, thus showing strong signals of the propagating radicals. Gamma irradiation of the frozen state produces a blue color in samples, and the ESR signals were found to be those of uninteracted acrylate and methacrylates. From a comparison of spectral widths, there seems to exist an intramolecular interaction between the radicals and the diacetylene group at the frozen state. © 1992 John Wiley & Sons, Inc.     

Spatial geometric arrangements of disulfide-crosslinked loops in nonplanar proteins

The method presented earlier [T. Kikuchi, G. Némethy, and H.A. Scheraga, (1986) J. Comput. Chem. 7 , 67] for the classification of patterns of the three-dimensional folding of a covalently crosslinked polypeptide chain has been extended to nonplanar proteins. The procedure described earlier was applicable only to proteins termed planar, i.e., with a connexity of the crosslinks (e.g., disulfide bonds) that can be represented in a planar diagram. The procedure described in the present work is applicable to any (planar or nonplanar) pattern of crosslinking. The classification is based on a systematic and objective method of enumeration of spatial geometric arrangements of loops (SGAL) using no information other than the location of the disulfide bonds in the amino acid sequence. Various SGAL classes correspond to the presence of different ways of mutual penetration of loops, called thrustings and entanglements. Information on SGAL classes can be of use in structural predictions of folding patterns of proteins.     

3-Aroylmethyl derivatives of 2(1H)quinoxalinone and 2H-l,4-benzoxazin-2-ones existing in the enamine form

Seventeen derivatives of 2(1H)quinoxalinone and 2H-l,4-benzoxazin-2-one have been synthesized for structural study. All of the compounds having a substituted phenacyl, isonicotinoylmethyl, or 2-furoylmethyl side chain are shown to exist in the enamine form with an internal chelation both in the crystalline and solution states as evidenced by the ir and pmr spectra, respectively. In the gas phase, however, o-hydroxyphenacyl derivatives can exist in another type of intramolecularly hydrogen-bonded form which is supported by their mass spectra.     

A theorem on the average number of subfaces in arrangements and oriented matroids

It is known that for simple arrangements in thed-dimensional Euclidean spaceR ^d The average number ofj-dimensional subfaces of ak-dimensional face is less than . In this paper, we show that this is also true for all arrangements inR ^d and for all oriented matroids, and we give combinatorial proofs.     

Optimization of in-gel protein digestion system in combination with thin-gel separation and negative staining in 96-well plate format

Improvement of in-gel digestion efficiency is highly desirable for one- or two-dimensional gel electrophoretic separation and mass spectrometric (MS) analysis in proteomics, because the resultant increases in sequence coverage and MS signal intensity lead to higher confidence in protein identification. Here an optimized in-gel digestion system, in combination with thin-gel separation and negative staining in a high-throughput format using 96-well plates, is described. The combination of negative staining and protein separation on a 0.9 mm thick gel showed a clear improvement in in-gel digestion efficiency in comparison with the more typical protocols such as the combination of silver staining and a 1.0 mm gel. In addition, the use of 96-well plates to increase throughput did not decrease the efficiency of this strategy when the stirring of the gel pieces in processes such as destaining, washing, gel-shrinking and peptide extraction was performed by sonication instead of shaking the plates. This procedure was optimized and applied to identify proteins of the postsynaptic density fraction; 105 proteins were identified after SDS-PAGE separation.