Chasing "Zampanalogs": Advancing the Synthesis of the Zampanolide Macrocycle

<p>(-)-Zampanolide (1), a natural product isolated from a marine sponge, is a microtubule-stabilizing agent that exhibits activity in the nanomolar range against various cancer cells, including in P-gp pump overexpressing cells. This attribute makes (-)-zampanolide an interesting target for further investigation. In this work, a new method for a modular and convergent total synthesis of optically pure zampanolide was investigated, which would also allow the generation of “zampanalogs” following the same basic strategy. Their biological activity may then be assessed to allow the elucidation of structure-activity relationships of (-)-zampanolide and its analogs in tubulin binding. The synthetic plan consisted of the modular combination of four major fragments, which would be connected in the late stages of the synthesis and could therefore be easily exchanged to allow the generation of analogs. The C15-C16 bond would be connected via an alkynylation reaction, and a subsequent reductive methylation would install the trisubstituted alkene. The connections at C1 and C3 could be achieved through a Bestmann ylid linchpin reaction, while the macrolactonization would be completed using a ring-closing metathesis to form the C8-C9 alkene. The side chain could be attached at C20 using one of the established aza-aldol methods. The fragments necessary for the formation of the macrocycle were synthesized successfully. The purification strategy throughout the synthetic route was rationalized and provides an improvement with respect to yield and time compared to work previously done in this research group. Alongside these fragments, modified fragments that were originally intended to serve as model systems were synthesized, which could also be used as building blocks in the synthesis of “zampanalogs”. Several methods for a stereoselective alkynylation at C15 were tested. These led to only meager successes, so an approach using a non-stereoselective alkynylation, followed by oxidation and a stereoselective CBS-reduction, was chosen. For the installation of the trisubstituted alkene a reductive methylation with vitride was tested, but this only led to the reduction of the alkyne without methylation. This product may be employed for the synthesis of C17-desmethyl analogs. The reductive methylation at C16-C17 was ultimately achieved using the Gilman reagent in a similar manner to the installation of the C5 methyl group in the C3-C8 fragment. A linchpin strategy with the Bestmann ylid simultaneously formed the connectivity at C1 and C3. This process was successfully performed on multiple substrates arising from the model systems used in the alkynylation and reductive methylation reactions, yielding precursors to the ring-closing metathesis and potentially enabling the synthesis of various analogs. The ring-closing metathesis proved to be difficult in analogs lacking the C17 methyl group and cis-tetrahydropyran ring, and due to this tendency further investigations are necessary. Once the macrocycle has been closed, a global deprotection and oxidation of hydroxy groups is necessary to allow for the installation of the sidechain.</p>

Chasing "Zampanalogs": Advancing the Synthesis of the Zampanolide Macrocycle

<p>(-)-Zampanolide (1), a natural product isolated from a marine sponge, is a microtubule-stabilizing agent that exhibits activity in the nanomolar range against various cancer cells, including in P-gp pump overexpressing cells. This attribute makes (-)-zampanolide an interesting target for further investigation. In this work, a new method for a modular and convergent total synthesis of optically pure zampanolide was investigated, which would also allow the generation of “zampanalogs” following the same basic strategy. Their biological activity may then be assessed to allow the elucidation of structure-activity relationships of (-)-zampanolide and its analogs in tubulin binding. The synthetic plan consisted of the modular combination of four major fragments, which would be connected in the late stages of the synthesis and could therefore be easily exchanged to allow the generation of analogs. The C15-C16 bond would be connected via an alkynylation reaction, and a subsequent reductive methylation would install the trisubstituted alkene. The connections at C1 and C3 could be achieved through a Bestmann ylid linchpin reaction, while the macrolactonization would be completed using a ring-closing metathesis to form the C8-C9 alkene. The side chain could be attached at C20 using one of the established aza-aldol methods. The fragments necessary for the formation of the macrocycle were synthesized successfully. The purification strategy throughout the synthetic route was rationalized and provides an improvement with respect to yield and time compared to work previously done in this research group. Alongside these fragments, modified fragments that were originally intended to serve as model systems were synthesized, which could also be used as building blocks in the synthesis of “zampanalogs”. Several methods for a stereoselective alkynylation at C15 were tested. These led to only meager successes, so an approach using a non-stereoselective alkynylation, followed by oxidation and a stereoselective CBS-reduction, was chosen. For the installation of the trisubstituted alkene a reductive methylation with vitride was tested, but this only led to the reduction of the alkyne without methylation. This product may be employed for the synthesis of C17-desmethyl analogs. The reductive methylation at C16-C17 was ultimately achieved using the Gilman reagent in a similar manner to the installation of the C5 methyl group in the C3-C8 fragment. A linchpin strategy with the Bestmann ylid simultaneously formed the connectivity at C1 and C3. This process was successfully performed on multiple substrates arising from the model systems used in the alkynylation and reductive methylation reactions, yielding precursors to the ring-closing metathesis and potentially enabling the synthesis of various analogs. The ring-closing metathesis proved to be difficult in analogs lacking the C17 methyl group and cis-tetrahydropyran ring, and due to this tendency further investigations are necessary. Once the macrocycle has been closed, a global deprotection and oxidation of hydroxy groups is necessary to allow for the installation of the sidechain.</p>

Protein Variation Associated With Facial Eczema Resistance or Susceptibility in Romney Sheep

<p>The detection of plasma and liver protein markers for facial eczema resistance or susceptibility in Romney sheep was undertaken. A pooling protocol was used to allow rapid comparison of variation between populations. A 2-D PAGE technigue was developed for protein separation. In general, proteins separated by 2-D PAGE were examined on Coomassie blue or silver stained gels. Greater sensitivity was achieved by labelling proteins with radioactive isotopes. Reductive methylation of the free amino groups of proteins with radioactively labelled formaldehyde and sodium cyanoborohydride was used for isotopic labelling of proteins. A double-labelling technique involving 14C and 3H was used to label plasma or liver proteins from facial eczema resistant and susceptible sheep. The labelled proteins were subsequently separated by 2-D PAGE and detected by autoradiography and fluorography. Any detected variation was further analysed for individuals on one-dimensional polyacrylamide gels which allowed more rapid analysis of multiple samples. No significant difference was detected among the liver proteins of resistant and susceptible sheep. However, among the approximately twenty major plasma protein families visualised on 2-D PAGE gels, significant variation between sheep selected for facial eczema resistance or susceptibility occurred at the transferrin locus. Sheep selected for resistance showed a predominance of acidic transferrins while sheep selected for susceptibility contained a basic transferrin in greater abundance. These results were confirmed and their significance was assessed by transferrin phenotyping on one-dimensional polyacrylamide gels. The transferrin A allele was more abundant in sheep selected for resistance while the transferrin D allele showed a greater association with facial eczema susceptibility. The A allele frequency was 0.57 in resistants and 0.05 in susceptibles while the D allele frequency was 0.18 in resistants and 0.68 in susceptibles. The results suggest some separation of transferrin A and D alleles between the animals selected for resistance and susceptibility. The basis of this variation is unknown. It may reflect either a physiological association of transferrin alleles with a character of importance in facial eczema resistance, or it may be a phenomenon unrelated to facial eczema resistance produced as a result of the way in which the facial eczema resistant and susceptible flocks were generated. It is expected that subsequent genetic studies will show whether transferrin phenotype can be used as a marker to select for facial eczema resistance as a means of controlling the disease.</p>

Protein Variation Associated With Facial Eczema Resistance or Susceptibility in Romney Sheep

<p>The detection of plasma and liver protein markers for facial eczema resistance or susceptibility in Romney sheep was undertaken. A pooling protocol was used to allow rapid comparison of variation between populations. A 2-D PAGE technigue was developed for protein separation. In general, proteins separated by 2-D PAGE were examined on Coomassie blue or silver stained gels. Greater sensitivity was achieved by labelling proteins with radioactive isotopes. Reductive methylation of the free amino groups of proteins with radioactively labelled formaldehyde and sodium cyanoborohydride was used for isotopic labelling of proteins. A double-labelling technique involving 14C and 3H was used to label plasma or liver proteins from facial eczema resistant and susceptible sheep. The labelled proteins were subsequently separated by 2-D PAGE and detected by autoradiography and fluorography. Any detected variation was further analysed for individuals on one-dimensional polyacrylamide gels which allowed more rapid analysis of multiple samples. No significant difference was detected among the liver proteins of resistant and susceptible sheep. However, among the approximately twenty major plasma protein families visualised on 2-D PAGE gels, significant variation between sheep selected for facial eczema resistance or susceptibility occurred at the transferrin locus. Sheep selected for resistance showed a predominance of acidic transferrins while sheep selected for susceptibility contained a basic transferrin in greater abundance. These results were confirmed and their significance was assessed by transferrin phenotyping on one-dimensional polyacrylamide gels. The transferrin A allele was more abundant in sheep selected for resistance while the transferrin D allele showed a greater association with facial eczema susceptibility. The A allele frequency was 0.57 in resistants and 0.05 in susceptibles while the D allele frequency was 0.18 in resistants and 0.68 in susceptibles. The results suggest some separation of transferrin A and D alleles between the animals selected for resistance and susceptibility. The basis of this variation is unknown. It may reflect either a physiological association of transferrin alleles with a character of importance in facial eczema resistance, or it may be a phenomenon unrelated to facial eczema resistance produced as a result of the way in which the facial eczema resistant and susceptible flocks were generated. It is expected that subsequent genetic studies will show whether transferrin phenotype can be used as a marker to select for facial eczema resistance as a means of controlling the disease.</p>

Reductive Methylation of Homogeneous Primary β-Lauryl/myristyl 7/3 Polyethyleneoxy n = 3–18 Ethylamines under Phase-Transfer Catalysis Conditions

Homogeneous tertiary N,N-dimethyl-N-β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylamines, LM(EO)nAT, are niche intermediates in the synthesis of homogeneous N-alkyl (C1–C18)-N,N-dimethyl-N-β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylammonium chlorides (unitary degree of oligomerization of ethylene oxide in the polyoxyethylene chain). This paper synthetically presents the dependence of the reductive methylation yields of homogeneous primary β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylamines, LM(EO)nAP, on the reaction time (10–90 min), the temperature (70 °C), the molar ratio formic aldehyde /LM(EO)nAP (1.1/1–2.5/1), the molar ratio HCOOH/LM(EO)nAP (5/1), the degree of oligomerization of ethylene oxide in the homogeneous polyoxyethylene chain in the 3,6,9,12,18 series, and the structure of the phase-transfer catalysts. The steric effects of hydrophobic groups CH3 and C18H37 grafted onto the ammonium function, and the micellar phenomena in the vicinity of their critical micellar concentration, directly proportional to the homogeneous degree of oligomerization, were highlighted. In all cases, a steady increase in reductive methylation yields was observed, with even quantitative values obtained. The high purity of the homologous series LM(EO)nAT will allow their personalization as reference structures for the study of the evolution of basic colloidal characteristics useful in forecasting technological applications. LM(EO)nAP were obtained either by direct amidoethylation (nucleophilic addition under basic catalysis of homogeneous lauryl/myristyl 7/3 polyethoxylated n = 3, 6, 9, 12, 18 alcohols, LM(EO)nOH, to acrylamide monomer) or by cyanoethylation of LM(EO)nOH under basic catalysis at 25–50 °C, in the presence of Fe2+ cations as oligomerization/polymerization inhibitor, followed by partial acid hydrolysis of homogeneous β-alkyl (C12H25/C14H29) 7/3 polyethyleneoxy n = 3, 6, 9, 12, 18 propionitriles, LM(EO)nPN, to β-alkyl (C12H25/C14H29) 7/3 polyethyleneoxy n = 3, 6, 9, 12, 18 propionamides, LM(EO)nPD, which led to LM(EO)nAP by Hoffmann degradation. Homogeneous higher tertiary polyetheramines LM(EO)nAT were structurally characterized.

Hydrophilic Quaternary Trimethyl Chitosan Stabilized Silver Nanoparticles: Synthesis, Characterization and Antimicrobial Activity.

Antimicrobial resistance (AMR) endangers the effective management of an increasing range of bacterial and fungal infections, alternative antimicrobial drugs are thus, expedient. In this study, Quaternary Trimethyl Chitosan (QTMC) was prepared by improved two step reductive methylation of Chitosan (CTS) employed as a capping agent for the synthesis of silver nanoparticles (QTMC-AgNPs). The hydrophilic QTMC and QTMC-AgNPs were characterized using various analytical and spectroscopic techniques. The Proton Nuclear Magnetic Resonance ( 1 HNMR) was used to determine the degree of quaternization (DQ) and degree of dimethylation (DT) of QTMC as 63.33 and 11.75 % respectively. The Ultraviolet-Visible (Uv-Vis), Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), X-ray Diffraction (XRD), Energy Dispersive X-ray (EDS) and X-ray Photoelectron (XPS) Spectroscopic results evidently indicated high degree of quaternization of CTS and configured QTMC-AgNPs. Thermogravimetric Analysis/Derivative Thermogravimetry (TGA/DTG) were used to study the decomposition process of QTMC and QTMC-AgNPs. The surface morphological difference of QTMC and QTMC-AgNPs was explored via Scanning Electron and High-Resolution Transmission Electron Microscopies (SEM and HR-TEM) whereas particle size distribution was analyzed using Dynamic Light Scattering. Furthermore, HR-TEM indicated QTMC stabilized AgNPs with average nanoparticulate size of 10 nm while DLS revealed 12.5 nm. This well-tailored QTMC-AgNPs exhibited strong antibacterial and antifungal activities against the tested bacteria and fungi infections.