The Avarol-Avarone Redox Behaviour in Acetonitrile

The oxidation of avarol and the reduction of avarone were studied at a Pt electrode in acetonitrile-tetraethyl-ammonium perchlorate media. The oxidation of avarol in acetonitrile takes place by formation of a two electron oxidation product, presumably the »protonated avarone«. The reduction of avarone takes place in two steps by formation of the stable radical anion which is reduced to the dianion at amore negative potential

Kinetika redukcije lipofilnog hinona avarona n-alkyl-1,4-di -hidronikotinamidima različite lipofilnosti

Several NADH model compounds, N-alkyl-1,4-dihydronicotinamides, some of them possessing amphiphilic properties, have been synthesized, and the kinetics of their reaction with a biologically active liphophilic quinone, avarone, has been studied in a protic solvent both in the presence and absence of cationic, anionic or non-ionic surfactants. In the absence of micellar agents, the medium-and long-chain N-dodecyl (3) and N-heptadecyl (4) derivatives show a significant increase in the reaction rates compared to other model compounds, due to the stabilization of the semiquinone intermediate. Anionic surfactants retard the reaction, non-ionic surfactants slightly accelerate the reaction with the short-chain derivatives, and retard the reaction with the medium-and long-chain derivatives, and the cationic surfactants increase the reaction rate with all derivatives except the long-chain 4. The results support the e-p-e mechanism of the reduction of lipophilic quinones by NADH models in protic medium.Sintetisano je nekoliko N-alkil-1,4-dihidronikotinamida, model-jedinjenja NADH, od kojih neki imaju amfifilne osobine, i proučavana je kinetika njihove reakcije sa biološkim aktivnim, lipofilnim hinonom avaronom u protinom rastvaraču u prisustvu katjonskih, anjonskih ili nejonskih površinski aktivnih supstanci i bez njh.Bez dodatih micelarnih agenasa, N-dodecil-derivat 3 (derivat srednje dužine niza) i dugolančani N-heptadecil-derivat 4 pokazuju značajno povećanje brzine reakcije u poređenju sa drugim model-jedinjenjima, usled stabilizacije semihinonskih intermedijera. Anjonski površinski aktivni agensi usporavaju reakciju, nejonski agensi dovode do slabog ubrzanja sa derivatima kratkog alkilniza, a usporavaju reak ciju sa derivatima srednjeg i dugog niza, dok katjonski agensi ubrzavaju reakciju sa svim derivatima, sem sa dugolančanim 4. Rezultati ukazuju na mehanizam e-p-e redukcije lipofilnih hinona modelima NADH u protičnom medijumu

Evaluation of the activity of the sponge metabolites avarol and avarone and their synthetic derivatives against fouling micro- and macroorganisms

The sesquiterpene hydroquinone avarol (1) was isolated from the marine sponge Dysidea avara, whereas the corresponding quinone, avarone (2), was obtained by oxidation of avarol, and the significantly more lipophilic compounds [3′-(p-chlorophenyl) avarone (3), 3′,4′-ethylenedithioavarone (4), 4′-isopropylthioavarone (5), 4′-tert-butylthioavarone (6), 4′-propylthioavarone (7), 4′-octylthioavarone (8)] were obtained by nucleophilic addition of thiols or p-chloroaniline to avarone. All these compounds were tested, at concentrations ranging from 0.5 to 50 μg/mL, for their effect on the settlement of the cyprid stage of Balanus amphitrite, for toxicity to both nauplii and cyprids and for their growth inhibitory activity on marine bacteria (Cobetia marina, Marinobacterium stanieri, Vibrio fischeri and Pseudoalteromonas haloplanktis) and marine fungi (Halosphaeriopsis mediosetigera, Asteromyces cruciatus, Lulworthia uniseptata and Monodictys pelagica)

An improved preparation of 3-α-acetoxy-11,20-diketo-(5β)-pregnane, the key intermediate in the synthesis of 11-oxygenated corticosteroids

Although microbiological methods of introducing oxygen at C-11 of the steroid molecule are effective, it is obvious that purely synthetic way of producing cortisone and its analogs from bile acids or hecogenin have never been abandoned. Thus, we succeeded to obtain 3alpha-L-acetoxy-11,20-diketo-(5-beta)-pregnane, the key intermediate in the synthesis of 11-oxygenated corticosteroids in a very improved yield exceeding 13% calculated on starting deoxycholic acid by the following sequence of reactions

Covalent modification of hexokinase by biologically active quinones

In this work, inhibition of sulfhydryl containing glycolytic enzyme hexokinase by avarone and its derivatives was studied. The enzyme contains lysine and sulfhydryl residues, which can be modified by the quinone moiety. Our results show that avarone and its derivatives are capable of covalent modification of hexokinase

Synthesis, structure, and reactions of secosteroids containing a medium-sized ring. Part 17. Structure-reactivity relationship in the solvolysis of 5,10-secosteroidal 3-tosylates

Kinetic measurements of the solvolysis of (Z)-3α- and (Z)-3β-, and (E)-3α- and (E)-3β-tosyloxy-5,10-secocholest-1(10)-en-5-ones in buffered aqueous acetone (90 : 10 v/v) reveal that the (Z)-3α-, (E)-3α-, and (E)-3β-tosylates are solvolysed according to a first-order rate law (the relative rates being ca. 1 : 3 : 8), while the (Z)-3β-ester, under the same conditions, reacts at a much slower rate by a complex mechanism, the kinetics of which are best approximated by a second-order law. These data and product analysis indicate that the former three esters are solvolysed with considerable double bond participation [resulting in the case of the (E)-3-esters in intramolecular cyclopropane ring closure], and that this interaction is unimportant for the (Z)-3β-tosylate. On the basis of conformational analysis of the starting tosylates and stereoelectronic requirements for homoallylic interaction, a possible mechanistic pathway for these solvolyses is proposed

A novel lectin from the sponge Haliclona cratera: isolation, characterization and biological activity

A lectin from the Adriatic sponge Haliclona cratera was purified by ion-exchange and gel chromatography The molecular mass of the lectin is approximately 29 kDa. Purified lectin is rich in hydrophobic and basic amino acids and has an isoelectric point at pH 8.6. H. cratera lectin is relatively heat- and pH-stable. It agglutinates native and trypsinized, papainized and neuraminidase-treated human A, B, O, AB and sheep erythrocytes, and the hemagglutinating activity is independent of Ca2+, Mn2+ and Mg2+ ions; D-galactose and N-acetyl-D-galactosamine are found to be moderate inhibitors of the activity. H. cratera lectin displays cytotoxic effect on HeLa and FemX cells and weak mitogenic effect on human T-lymphocytes pretreated with phytohemagglutinin (PHA). (C) 2002 Elsevier Science Inc. All rights reserved

Structure-reactivity relationship in the solvolysis of 5,10-secosteroidal 5-p-nitrobenzoates

The solvolysis of (Z)- and (E)-3β-acyloxy-5,10-seco-1(10)-cholesten-5β-ol p-nitrobenzoates 4 and 5 has been investigated and compared with the solvolytic reactivity of the epimeric (Z)- and (E)-5α-p-nitrobenzoates 1 and 2, as well as of the reference compound, i.e. the 1,10-saturated 5α-p-nitrobenzoate. Kinetic data and product analysis revealed that the relative spatial orientation of the 1(10)-olefinic double bond and the chiral center at C(5) in the 10-membered ring, which these secosteroidal 5-p-nitrobenzoates can adopt in the transition state, is the main factor which determines their solvolytic behaviour, so that the esters 1,2 and 5 solvolyse with transannular double bond participation, while such an interaction is not present in the case of the (Z)-5β-ester 4. © 1979