Showing papers in "Molecules in 1996"

Molecular Diversity Assessment: Logarithmic Relations of Information and Species Diversity and Logarithmic Relations of Entropy and Indistinguishability after Rejection of Gibbs Paradox of Entropy of Mixing

Abstract: It is postulated that the degradation of species diversity results in information loss or entropy increase. To define the molecular diversity of either a single mixture of different compounds and a combinatorial compound library or a collection of pure compounds, we treat them all as molecular assemblages for information registration and consider only the molecular similarity and chemical species numbers of the individual molecules. The entropy of a molecular assemblage is correlated to the chemical species similarity via the von Neumann-Shannon relation and related to the so-defined apparent species indistinguishability number (σ a ) via a logarithmic relation. Information and the apparent species number ( M a ) also have a logarithmic relation. M a is equal to or less than the designated species number M. The diversity index (D) is defined as the ratio of the logarithms of the apparent chemical species number and the designated species number (D=lnM a /lnM). D has a value between 0 and 1 and decreases with the increase in similarity among the species. The decrease in the evenness of the species abundance also results in a decrease in diversity D. Molecular diversity of a combinatorial compound library is determined by the available number of component variants and their similarity. Clearly these concepts and formulae can also be applied to calculate biodiversity.

Synthesis of 3,6-Disubstituted Tetrahydro-S-triazolo[3,4-b][1,3,5]thiadiazines

Abstract: Ten novel 3,6-disubstituted tetrahydro-S-triazolo[3,4-b][1,3,5]thiadiazines 2 have been synthesized by the double Mannich reaction of 3-aryl-5-mercapto-1,2,4-triazole with various aromatic amines and formaldehyde in the presence of ethanol-HCl solution. The structure of these compounds was determined by elemental analysis, IR, NMR and MS. Their antibacterial activities against E. coli, B. bob and S. aureus have been tested.

Leucine and Isoleucine Conjugates of 1-Oxo-2,3-dihydro-indene-4-carboxylic Acid: Mimics of Jasmonate Type Signals and the Phytotoxin Coronatine

Abstract: Leucine and isoleucine conjugates of 1-oxo-2,3-dihydro-indene-4-carboxylic acid (1-oxo-ICA) such as 2a-e are powerful elicitors of volatile biosynthesis in the Lima bean (Phaseolus lunatus). The compounds are structurally and, with a few exceptions, functionally related to coronatin 1, a phytotoxin from pathovars of Pseudomonas spp. Coronatin 1 and the conjugates of 1-oxo-ICA 2a-e seem to mimic signals from the octadecanoid signalling pathway, like, for example, amino acid conjugates of jasmonic acid.

Application of the 1, n -ADEQUATE Experiment in the Assignment of Highly Substituted Aromatic Compounds

Abstract: This communication describes the application of the 1, n-ADEQUATE experiment to differentiate between the two possible products ( 4 and 5) of an acylation reaction of starting material 3. The ADEQUATE experiments are new NMR based methods for assigning the constitution of natural products, combining a HSQC or HMBC step with a C,C correlation in natural abundance. The 1, n-ADEQUATE technique allows to observe pseudo J CH correlations which were necessary for the distinction of 4 and 5. Different NMR methods for the constitutional assignment of natural products and other organic molecules are discussed in detail. This communication also demonstrates that the 1, n-ADEQUATE method is generally applicable for the constitutional assignment of highly substituted aromatic compounds as well as for the localization of O-acetyl groups bound to quarternary carbons.

Editorial: A Good Yield and a High Standard

Abstract: publishes peer-reviewed research papers on synthetic chemistry and naturalproduct chemistry. The rapid publication schedule requires that authors make sure their submitted or revisedmanuscripts are in the final form. In order to comply with this requirement, I considered treating theCorrigendum column as an advertisement and charging all authors who contribute to it. If

A Good Yield and a High Standard

Abstract: The new journal Molecules publishes peer-reviewed research papers on synthetic chemistry and natural product chemistry.[...]

Synthesis of Spiroketals Related to Griseusin A

Abstract: The synthesis and attempted functionalization of the spiroketal ring system of the naturally occurring pyranonaphthoquinone antibiotic griseusin A 1 is reported. The unsaturated spiroketals 5,6 were prepared from furonaphthopyran 22, which in turn was constructed from furonaphthofuran 20. Addition of 2-trimethylsilyloxyfuran 13 to quinone 19 afforded furonaphthofuran 20. Initial work using acetylenic quinone 12 afforded a pentacyclic product 15, where a third Michael reaction of the phenolic hydroxyl group with the α,β-unsaturated ketone moiety had occurred. Modified reaction conditions afforded trimethylsilyl analogue 16. Naphthoquinone 19, which bears a 2-alkenyl side chain rather than an acetylene, was synthesized using similar methodology to 12 and subsequently converted to furonaphthofuran adduct 20. Ceric ammonium nitrate oxidative rearrangement of 20 produced diol 22, which was then cyclized to spiroketals 5,6 under acidic conditions. Reaction of spiroacetals 5,6 with osmium tetroxide did not effect the desired hydroxylation of the olefin. Use of cetyltrimethylammonium permanganate as the hydroxylation reagent resulted in reaction with the C5a-C11a double bond affording diols 24,25.

Hydration of Acetylenic Esters: Synthesis of β ββ ββ-Keto-Esters

Abstract: Acetylenic esters, which are easily prepared by carbethoxylation of terminal acetylenes, can be hydrated regioselectively to β-keto-esters. In this paper, the terminal acetylenes were prepared by addition of lithium acetylide (complexed with ethylenediamine) to epoxides of cyclopentane derivatives to produce compounds oxygenated at the same position as certain natural products from Otoba parvifolia. The hydration was carried out by two different processes, producing either δ-oxygenated or γ,δ-unsaturated β-keto-esters.