A new phenanthrene lactam, designated as velutinam (10-amino-8-hydroxy-3,4-dimethoxyphenanthrene-1-carboxylic acid lactam), was isolated from an extract of the bark of Goniothalamus velutinus, along with aristolactam-BII (10-amino-3,4-dimethoxyphenanthrene-1-carboxylic acid lactam). Their structures were established from spectral data.

Malaysiatin (1), the first homodetic cycloheptapeptide from a marine source, has been isolated from the cytotoxic and antimicrobial extracts of the marine sponge Pseudaxinyssa sp., collected in Borneo. The unusual structure of malaysiatin, which contains homodipeptide and homotripeptide fragments, was elucidated by extensive spectroscopic analysis that suggests an all-L stereochemistry.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDrawing Lewis structures: A step-by-step approachWan-Yaacob Ahmad and Siraj Omar Cite this: J. Chem. Educ. 1992, 69, 10, 791Publication Date (Print):October 1, 1992Publication History Received3 August 2009Published online1 October 1992Published inissue 1 October 1992https://doi.org/10.1021/ed069p791RIGHTS & PERMISSIONSArticle Views843Altmetric-Citations15LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Two major compounds have been isolated and characterized from the roots of Goniothalamus uvaroides: goniothalamin, a biologically active styryl dihydropyrone, and its derivative, 5-acetyl goniothalamin. The isolation of goniothalamin has been previously reported from several Goniothalamus species collected from Peninsular Malaysia, Sabah and Sarawak. However, 5-acetyl goniothalamin has never been reported before. Structure elucidation of these compounds was carried out by spectroscopic methods.

Cyclic peptides, fenestins A ( 1 ), B ( 2 ) and a known diketopiperazine, cyclo -(L-Pro-L-Val) ( 3 ) are reported from the sponge Leocophloeus fenestrata .

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPolyfunctional diterpene isonitriles from marine sponge Acanthella carvenosaSiraj Omar, Carolyn Albert, Tashin Fanni, and Phillip CrewsCite this: J. Org. Chem. 1988, 53, 25, 5971–5972Publication Date (Print):December 1, 1988Publication History Published online1 May 2002Published inissue 1 December 1988https://pubs.acs.org/doi/10.1021/jo00260a034https://doi.org/10.1021/jo00260a034research-articleACS PublicationsRequest reuse permissionsArticle Views141Altmetric-Citations38LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

The low field portion of the 360 MHz 1H nuclear magnetic resonance spectrum of phenylmethanesulfonyl-subtilisin Novo (EC 3.4.21.14) has been studied as a function of pH. Analysis of the pH-induced chemical shift changes occurring between 6 to 7 ppm revealed five classes of ionizable residues with pK values (uncorrected) of 10.3, 10.7, 10.7, 10.8, and 11.0. With a single exception the titration curves can be fit by assuming a simple proton ionization equilibrium. Four classes of low intensity broad resonances, assigned to the histidyl residues, are observed between 8 and 9 ppm. Uncorrected pK values of 5.4, 5.7, 6.0, and 6.4 were determined for the residues comprising each of these classes. The spectral data are consistent with protonation of one or more histidyl residues upon acid induced denaturation of the protein. These results are compared with those of analogues studies performed by the use of other techniques.

The tyrosyl and tryptophyl fluorescence of diisopropylphosphorylsubtilisins Carlsberg and Novo, respectively, is quenched efficiently by I- but is not significantly affected by Cs+. The I-quenching data were analyzed using a modified Stern-Volmer treatment (Lehrer, S.S. (1971), Biochemistry 10, 3254), yielding values for the effective fraction of accessible protein fluorescence of 90-95 and 88-92% for the tyrosyl and tryptophyl emission of diisopropyl-phosphorylsubtilising Carlsberg and Novo, respectively. Similar values were obtained pH 5 and 7. The effective collisional quenching constant depends on pH in a manner suggesting the participation of protein surface charge in the quenching mechanism. Significant singlet energy transfer (efficiency = 0.52) from tyrosyl to tryptophyl residues was inferred from the excitation spectra of diisopropylphosphorylsubtilisn Novo. The very low efficiency of energy transfer to Trp-113 in diisopropylphorphorylsubtilisin Carlsberg suggests that Trp-105 and Trp-241 are the acceptors of tyrosyl emission in the homologous Novo enzyme. The unusually low quantum yield of Trp-113 in diisopropylphosphorylsubtilisin Carlsberg together with the tryptophyl fluorescence quenching behavior of the Novo enzyme suggests that this residue is "buried" and in accessible to quenching in both enzymes. The tyrosyl quenching behavior of diisopropylphorphorylsubtilisin Carlsberg is consistent with the high degree of solvent exposure of aromatic residues evident in the X-ray model of subtilisin Novo.