Nanofilm allotrope and phase transformation of ultrathin Bi film on Si(111)-7x7

Our scanning tunneling microscopy and electron diffraction experiments revealed that a new two-dimensional allotrope of Bi forms on the Si(111)-7x7 surface. This pseudocubic [012]-oriented allotrope is stable up to four atomic layers at room temperature. Above this critical thickness, the entire volume of the film starts to transform into a bulk single-crystal (001) phase, as the bulk contribution in the cohesion becomes dominant. Based on ab initio calculations, we propose that the new allotrope consists of black phosphorus-like puckered layers stabilized by saturating all the p(z) dangling bonds in the film.

Sporostatin, a novel and specific inhibitor of EGF receptor kinase

Sporostatin isolated from a fungus of Sporormiella sp.M5032 as an inhibitor of cyclic adenosine 3',5'-monophosphate phosphodiesterase, was found to be a specific inhibitor of epidermal growth factor (EGF) receptor tyrosine kinase in vitro. Its IC50 values were 0.1 microgram/ml (0.38 microM) for EGF receptor kinase, 3 micrograms/ml (11 microM) for ErbB-2, and 100 micrograms/ml (380 microM) or more than that for other kinases including PDGF receptor, v-src and protein kinase C. Kinetic analyses revealed that inhibition of EGF receptor kinase by sporostatin was noncompetitive either with substrate or with ATP. Autophosphorylation of EGF receptor in A431 cells was also inhibited. These results show that sporostatin is a potent and specific inhibitor of EGF receptor kinase.

New neplanocin analogues. IX. A practical preparation of (6'R)-6'-C-methylneplanocin A (RMNPA), a potent antiviral agent, and the determination of its 6'-configuration. Diastereoselective deamination by adenosine deaminase

We previously synthesized (6'R)- and (6'S)-6'-C-methylneplanocin A's (2a and 2b, respectively), and found that one of them has a potent antiviral activity, though its 6'-configuration has not been confirmed. This report describes the determination of the 6'-configuration and practical preparation of the antivirally active diastereomer. The 6'-configuration of the active diastereomer was determined as R by the modified Mosher's method as well as by synthesizing 2b from the known cyclopentenone derivative 10. A practical method for preparing the 6'R-diastereomer was developed by using diastereoselective deamination with Ado deaminase as the key step. Treatment of the diastereomeric mixture of 2a and 2b, which was prepared via an addition reaction of Me3Al with the 6'-formyl derivative 3, with Ado deaminase from calf intestine, deaminated 2b selectively to give the corresponding (6'S)-inosine congener 5, and left the desired 2a not deaminated. After silica gel column chromatography, 2a was obtained in a pure form.

Stachybocins, novel endothelin receptor antagonists, produced by Stachybotrys sp. M6222. I. Taxonomy, fermentation, isolation and characterization

Stachybocins A, B and C, novel endothelin (ET) receptor antagonists, were isolated from the culture filtrate of Stachybotrys sp. M6222. They were extracted with ethyl acetate and then purified by alumina and silica gel column chromatographies. The molecular formulae of stachybocins were determined to be C52H70N2O10 (stachybocin A) and C52H70N2O11 (stachybocins B and C). It was supposed that they consisted of spirobenzofuran and terpene units from NMR spectra. They showed the inhibitory activity of 125I-ET-1 binding to rate ETA, human ETA and human ETB receptors.

Stachybocins, novel endothelin receptor antagonists, produced by Stachybotrys sp. M6222. II. Structure determination of stachybocins A, B and C

The structures of stachybocins A, B and C, new endothelin receptor antagonist, were determined by NMR spectral analysis using pulse-field-gradient technique. Stachybocin A consists of two spirobenzofuran units each fused to a substituted decalin, which were connected by a lysine residue. Stachybocins B and C are derivatives of stachybocin A with an additional hydroxy group at the same position in the different decalin unit.

New neplanocin analogues. IV. 2-Fluoroneplanocin A: an adenosine deaminase-resistant equivalent of neplanocin A

2-Fluoro- and 2-chloroneplanocin A's (2 and 3) were synthesized as an adenosine deaminase resistant-equivalent of neplanocin A, and evaluated for their antitumor and antiviral activities. Of these, 2 was completely resistant to adenosine deaminase and showed more significant antitumor and antiviral activities than neplanocin A.

Use of transcriptional-enhancer elements responsive to ras, protein kinase A and protein kinase C to evaluate inhibitors of specific signal transduction pathways

To evaluate ras-mediated signal transduction, we constructed a transient transfection assay system that measures chloramphenicol acetyl transferase activity expressed under the transcriptional-enhancer elements responsive to ras, protein kinase C, and protein kinase A in NIH3T3 cells. Characterization of the assay system with several known activators and inhibitors of signal transduction pathways proved that our system could reliably evaluate agents that affect individual pathways. Pirarubicin ((2"R)-4'-tetrahydropyranyladriamycin, THP), which has recently been found able to reverse ras-transformed cells, appeared to selectively inhibit the ras signal transduction pathway.

Method of identifying inhibitors of oncogenic transformation: selective inhibition of cell growth in serum-free medium

We developed a new method for evaluating inhibitors of oncogenic signal transduction pathways based on different growth abilities between normal and transformed cells in a defined serum-free medium. The growth rates of src, abl or ras oncogene-transformed cells, activated raf proto-oncogene transformed cells, and normal NIH-3T3 cells were 60-90%, 20-30% and 10% in a serum-free medium, respectively, compared to the growth rates in a serum-containing medium. An addition of a growth factor (PDGF, FGF or TGF-beta) stimulated the growth of normal NIH3T3 cells by 40-80% in a serum-free medium. Herbimycin A, a specific cytoplasmic protein tyrosine kinase inhibitor, selectively inhibited the growth of src or abl transformed cells in the serum-free medium resulting in about 10-fold or fivefold lower IC50 than those in the serum-containing medium. The antibiotic did not show such an effect on ras transformed cells, and the treatment of src transformed cells with other protein kinase inhibitors or cytotoxic drugs showed little IC50 shifts between the two media. Thus, this method of comparing growth inhibition in the serum-free and the serum-containing media may be useful in evaluating specific inhibitors of signaling pathways mediated by growth factors and certain oncogene products.

Sporeamicin A, a new macrolide antibiotic. I. Taxonomy, fermentation, isolation and characterization

Sporeamicin A, a novel antibiotic, was isolated from the culture filtrate of an actinomycete. The producing organism, strain L53-18, was taxonomically assigned as a species of the genus Saccaropolyspora. The antibiotic was extracted with chloroform and was then purified by crystallization. It was obtained as colorless prisms from ethanolic solutions. Sporeamicin A exhibited a strong UV absorption peak at 276 nm. The molecular formula of sporeamicin A was determined to be C37H63NO12.

Sporeamicin A, a new macrolide antibiotic. II. Structure determination

Structure of a novel antibiotic, sporeamicin A (SRM-A), was determined by a combination of spectroscopic and X-ray crystallographic studies. SRM-A has a unique structure containing a 2,3-dihydro-3-oxofuran moiety as part of a 14-membered macrolide ring.

Sporeamicin A, a new macrolide antibiotic. III. Biological properties

Sporeamicin A is a new erythromycin-type antibiotic isolated from a species of Saccharopolyspora. It was active in vitro against a wide variety of Gram-positive bacteria. In vitro studies indicated that the sporeamicin A was stable in the presence of human serum, although it was bound to serum proteins. Sporeamicin A was effective in the mouse protection test against Staphylococcus aureus, Streptococcus pyogenes and Streptococcus pneumoniae. Sporeamicin A attained higher plasma and tissue levels in the rat than did erythromycin stearate.

Two-stage model of visual pattern discrimination learning in macaque monkeys (Macaca mulatta and Macaca fuscata)

To investigate the nature underlying the process of pattern discrimination learning, a series of seven experiments on seven working assumptions were undertaken. The main findings are as follows. The pattern discrimination learning consists of two time-dependent stages: The initial or first learning stage is the period of performance at chance, and the succeeding or second stage is the period of performance from just above the chance to a criterion level. The duration of the first stage is dependent on the degrees of cue-response separations, whereas that of the second stage is independent of. During the first stage, monkeys do not attend to the discriminative cue even at small cue-response separations, whereas during the second stage, they achieve pattern discrimination, or pattern perception and cognition, regardless of cue-response separations. After having learned the first pattern task with a cue-response separation, they learned new pattern tasks by means of the second stage, showing marked saving of the duration of the first stage. The findings in the present studies indicate that the first stage of learning is predominantly involved in the process of attending to the discriminative cues remote from the response site (a selective attention to the cue), whereas the second stage is concerned with the process of perception and cognition of the discriminative cue.

Isolation and characterization of new thiol protease inhibitors estatins A and B

New thiol protease inhibitors, estatins A and B, were isolated from the culture filtrate of Myceliophthora thermophila M4323. The basic, water-soluble inhibitors were characterized as having an agmatine, trans-epoxysuccinic acid and L-phenylalanine or L-tyrosine moieties in the structure. The molecular formulas C18H25N5O5 and C18H25N5O6 for A and B were indicated by elemental analysis and fast atom bombardment MS. Estatins were specific inhibitors against thiol proteases such as papain, ficin and bromelain. They suppressed IgE antibody production in mice, but not IgG.

Effect of small cue-response separation on pattern discrimination in macaques (Macaca fuscata and M. mulatta)

In order to elucidate the nature of the effect of small cue-response separations on pattern discriminations by monkeys, three studies were performed. When training on a pattern discrimination with a cue-response separation was discontinued during performance at the chance level, there was no saving on the rate of learning a second task (with identical cues but a different cue-response separation) relative to the performance of naive control animals. By contrast, when training was discontinued at a performance level a little better than chance, there was significant saving on learning a second task. After learning the second task, a third task with new pattern cues was learned, with marked saving on the duration of performance at the chance level. The results indicate that during the initial stage of performance at the chance level, monkeys do not attend to cues if there is even a small separation between the cue and the response site.

Acquisition of discrimination learning of patterns identical in configuration in macaques (Macaca mulatta and M. fuscata)

The acquisition of discrimination of five pairs of pattern cues in a Wisconsin General Testing Apparatus by 223 naive macaque monkeys was compared. The pairs of discriminanda were identical in configuration but varied slightly in either the size of the cue or the size of the background plaque; thus, the degree of separation of the cue from the fringe of the plaque, the response site, was slightly different for each pair of discriminanda. These small differences in cue-response separation had marked effects on the rate of acquisition of the discriminations. Even an increment of separation as small as 0.5 cm resulted in a remarkable retardation of the acquisition. This retardation was due entirely to prolonged performance at the chance level, and not to a slow rate of improvement from the chance to a criterion level. The finding indicates that the difficulty in the acquisition learning on pattern tasks depends largely on the difficulty of attending to the pattern cues at small cue-response separations.

Further evidence on elevated discrimination limens for reduced patterns in monkeys with inferotemporal lesions

An attempt was made to elucidate the nature and neural basis of the elevated discrimination limen for visual stimuli of reduced sizes that had been discovered earlier in monkeys with inferotemporal lesions. Although anterior inferotemporal damage was found to have only negligible effect, both total inferotemporal and posterior inferotemporal lesions yielded markedly elevated limens for reduced pattern stimuli but not for reduced colour stimuli. The impaired animals could be trained to discriminate reduced patterns that were below their original discrimination limen, but this required many more trials than were needed for postoperative relearning of the initial pair; normal animals, by contrast, showed perfect transfer from the standard to the smallest pair. The findings suggest that the increased threshold for reduced patterns in monkeys with inferotemporal lesion is attributable not to a visual acuity disorder but to an impairment of pattern perception resulting mainly from damage to posterior inferotemporal cortex.

Studies on neplanocin A, new antitumor antibiotic. II. Structure determination

The structure and stereochemistry of neplanocin A was determined on the basis of its spectral and chemical evidences as [1R-(la,2a,3b)]-3-(6-amino-9-yl)-5-(hydroxy-methyl)-4-cyclopentene-1,2-diol. For the final proof of the structure, X-ray crystallographic analysis of neplanocin A was carried out.

Studies on neplanocin A, new antitumor antibiotic. I. Producing organism, isolation and characterization

Neplanocin A. C11H13N5O3, is a novel carbocyclic analog of adenosine with cyclopentene. It was isolated from the culture filtrate of Ampullariella regularis A11079 by means of ion-exchange, carbon, silica gel adsorption, or partition chromatography. Neplanocin A forms crystals, and is stable at acidic or alkaline pH. Neplanocin A has cytotoxicity against L5178Y cells in culture and showed a remarkable effect on the life prolongation of mice infected with L1210 leukemia.

Plasmid-mediated penicillin beta-lactamases in Pseudomonas aeruginosa

A penicillin beta-lactamase (PCase) was extracted from Pseudomonas aeruginosa Rms139(+) and purified by means of column chromatography. The isoelectric point of Rms139 PCase was 5.7 and its molecular weight was 22,500 +/- 1,000. The optimal pH for the hydrolysis of benzylpenicillin was 7.0 to 7.5 and the optimal temperature was 45 C, with the PCase also showing high activity against carbenicillin. It is concluded that this enzyme is a new type of penicillin beta-lactamase different from the type I, II, or III R plasmid-mediated PCases reported previously.