76
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Nyongbela KD, Makolo FL, Hoye TR, Efange SMN. Isolation and Characterization of Sclerienone C from Scleria Striatinux. Nat Prod Commun 2016. [DOI: 10.1177/1934578x1601100102] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Herein, we report the isolation and characterization of sclerienone C, a novel sesquiterpene isolated from the methylene chloride/methanol (1:1) extract of Scleria striatinux that we have deduced to have structure 1. This medicinal spice of Cameroon has been shown to display antimicrobial and antiplasmodial activities. The isolation and purification involved a combination of methods including silica gel column chromatography, Sephadex LH-20, and semi-prep HPLC separations. Structure elucidation was carried-out by means of spectroscopic analysis and comparison with previously isolated sesquiterpene derivatives from the plant.
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77
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Wiitala KW, Hoye TR, Cramer CJ. Hybrid Density Functional Methods Empirically Optimized for the Computation of (13)C and (1)H Chemical Shifts in Chloroform Solution. J Chem Theory Comput 2015; 2:1085-92. [PMID: 26633067 DOI: 10.1021/ct6001016] [Citation(s) in RCA: 127] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Two hybrid generalized-gradient approximation density functionals, WC04 and WP04, are optimized for the prediction of (13)C and (1)H chemical shifts, respectively, using a training set of 43 molecules in chloroform solution. Tests on molecules not included in the training set, namely six stereoisomeric methylcyclohexanols and a β-lactam antibiotic, indicate the models to be robust and moreover to provide results more accurate than those from equivalent B3LYP, PBE1, or mPW1PW91 calculations, particularly for the prediction of downfield resonances in nuclear magnetic resonance spectra. However, linear regression of the B3LYP, PBE1, and mPW1PW91 predicted values on the experimental data improves the accuracy of those models so that they are comparable to WC04 and WP04.
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78
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Marell DJ, Furan LR, Woods BP, Lei X, Bendelsmith AJ, Cramer CJ, Hoye TR, Kuwata KT. Mechanism of the Intramolecular Hexadehydro-Diels-Alder Reaction. J Org Chem 2015; 80:11744-54. [PMID: 26270857 PMCID: PMC4729778 DOI: 10.1021/acs.joc.5b01356] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Theoretical analysis of the mechanism of the intramolecular hexadehydro-Diels-Alder (HDDA) reaction, validated against prior and newly measured kinetic data for a number of different tethered yne-diynes, indicates that the reaction proceeds in a highly asynchronous fashion. The rate-determining step is bond formation at the alkyne termini nearest the tether, which involves a transition-state structure exhibiting substantial diradical character. Whether the reaction then continues to close the remaining bond in a concerted fashion or in a stepwise fashion (i.e., with an intervening intermediate) depends on the substituents at the remaining terminal alkyne positions. Computational modeling of the HDDA reaction is complicated by the significant diradical character that arises along the reaction coordinate, which leads to instabilities in both restricted singlet Kohn-Sham density functional theory (DFT) and coupled cluster theory based on a Hartree-Fock reference wave function. A consistent picture emerges, however, from comparison of broken-symmetry DFT calculations and second-order perturbation theory based on complete-active-space self-consistent-field (CASPT2) calculations.
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79
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Han J, Michel AR, Lee HS, Kalscheuer S, Wohl A, Hoye TR, McCormick AV, Panyam J, Macosko CW. Nanoparticles Containing High Loads of Paclitaxel-Silicate Prodrugs: Formulation, Drug Release, and Anticancer Efficacy. Mol Pharm 2015; 12:4329-35. [PMID: 26505116 DOI: 10.1021/acs.molpharmaceut.5b00530] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have investigated particle size, interior structure, drug release kinetics, and anticancer efficacy of PEG-b-PLGA-based nanoparticles loaded with a series of paclitaxel (PTX)-silicate prodrugs [PTX-Si(OR)3]. Silicate derivatization enabled us to adjust the hydrophobicity and hydrolytic lability of the prodrugs by the choice of the alkyl group (R) in the silicate derivatives. The greater hydrophobicity of these prodrugs allows for the preparation of nanoparticles that are stable in aqueous dispersion even when loaded with up to ca. 75 wt % of the prodrug. The hydrolytic lability of silicates allows for facile conversion of prodrugs back to the parent drug, PTX. A suite of eight PTX-silicate prodrugs was investigated; nanoparticles were made by flash nanoprecipitation (FNP) using a confined impingement jet mixer with a dilution step (CIJ-D). The resulting nanoparticles were 80-150 nm in size with a loading level of 47-74 wt % (wt %) of a PTX-silicate, which corresponds to 36-59 effective wt % of free PTX. Cryogenic transmission electron microscopy images show that particles are typically spherical with a core-shell structure. Prodrug/drug release profiles were measured. Release tended to be slower for prodrugs having greater hydrophobicity and slower hydrolysis rate. Nanoparticles loaded with PTX-silicate prodrugs that hydrolyze most rapidly showed in vitro cytotoxicity similar to that of the parent PTX. Nanoparticles loaded with more labile silicates also tended to show greater in vivo efficacy.
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80
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Ayyad SEN, Hoye TR, Alarif WM, Al Ahmadi SM, Basaif SA, Ghandourah MA, Badria FA. Differential cytotoxic activity of the petroleum ether extract and its furanosesquiterpenoid constituents from Commiphora molmol resin. ACTA ACUST UNITED AC 2015; 70:87-92. [PMID: 26020558 DOI: 10.1515/znc-2014-4191] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Accepted: 04/26/2015] [Indexed: 11/15/2022]
Abstract
This study revealed a differential cytotoxic activity of the petroleum ether extract (IC₅₀ =5 μg/mL) of the resinous exudates of Commiphora molmol against two mouse cell lines KA31T and NIH3T3 (untransformed and transformed mouse fibroblasts, respectively). Four new compounds (1-4) and five known compounds (5-9) were isolated from the petroleum ether extract. The identity of these new compounds was determined as γ-elemane lactone (1), 5-αH,8-βH-eudesma-1,3,7(11)-trien-8,12-olide (2), 2-hydroxy-11,12-dihydrofuranodiene (3), and 2-hydroxyfuranodiene (4). 1 and 2 displayed the highest cytotoxic activity against NIH3T3 cells. 7 and 9 exhibited moderate cytotoxic activity against KA31T cells. Compounds 3-6 showed weak cytotoxic activities against both cell lines. These results may explain the high efficacy of the petroleum ether fraction in several myrrh-derived pharmaceutical preparations.
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81
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Wang T, Hoye TR. Diels-Alderase-free, bis-pericyclic, [4+2] dimerization in the biosynthesis of (±)-paracaseolide A. Nat Chem 2015. [PMID: 26201740 PMCID: PMC4878989 DOI: 10.1038/nchem.2281] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The natural product paracaseolide A is a tetracyclic dilactone containing six adjacent stereocenters. It has an unprecedented skeleton and occupies unique structural space among the >200,000 characterized secondary metabolites. Six different research groups have reported a chemical synthesis of this compound, five of which used a thermal, net Diels–Alder [4+2] cycloaddition and dehydration at 110 °C to access the target by dimerization of a simple butenolide precursor. Here we report that this dimerization proceeds under much milder conditions and with a different stereochemical outcome than previously recognized. This can be rationalized by invoking a bis-pericyclic transition state. Furthermore, we find that spontaneous epimerization, necessary to correct the configuration at one key stereocenter, is viable and that natural paracaseolide A is racemic. Together these facts point to the absence of enzymatic catalysis (i.e., Diels–Alderase activity) in the cycloaddition and strongly suggest that a non-enzyme-mediated dimerization is the actual event by which paracaseolide A is produced in Nature.
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82
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Nguyen QL, Baire B, Hoye TR. Competition between classical and hexadehydro-Diels-Alder (HDDA) reactions of HDDA triynes with furan. Tetrahedron Lett 2015; 56:3265-3267. [PMID: 26028780 DOI: 10.1016/j.tetlet.2014.12.053] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We report here thermal reactions between furan and one of three related triyne substrates. Each triyne is capable of reacting initially in two modes: (i) unimolecular hexadehydro-Diels-Alder (HDDA) reaction or (ii) bimolecular Diels-Alder reaction between one of its alkynes with furan. The relative rates of these initial events are such that two of the substrates react essentially in only one of modes (i) or (ii). The third is intermediate in behavior; its bifurcation is dependent on the concentration of the furan reactant. These results teach, more generally, principles relevant to the design of efficient HDDA-based reaction cascades.
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83
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Hoye TR, Alarif WM, Basaif SS, Abo-Elkarm M, Hamann MT, Wahba AE, Ayyad SEN. New cytotoxic cyclic peroxide acids from Plakortis sp. marine sponge. ARKIVOC 2015; 2015:164-175. [PMID: 26835518 PMCID: PMC4732738 DOI: 10.3998/ark.5550190.p008.948] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
Bioassay-guided fractionation of the extract of Jamaican marine sponge Plakortis sp. followed by preparative TLC and HPLC yielded several known methyl ester cyclic peroxides (1a, 2a, 3a, 4, 5), known plakortides (6,7), known bicyclic lactone (8) and new cyclic peroxide acids (1b, 2b, 3b). The chemical structures were elucidated by extensive interpretation of their spectroscopic data. These natural products showed remarkable in vitro cytotoxicity against several cancer cell lines.
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84
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Pogula VD, Wang T, Hoye TR. Intramolecular [4 + 2] trapping of a hexadehydro-Diels-Alder (HDDA) benzyne by tethered arenes. Org Lett 2015; 17:856-9. [PMID: 25671804 DOI: 10.1021/ol5037024] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report here the efficient, intramolecular trapping in a Diels-Alder (DA) sense of thermally generated benzynes by one of two pendant arene rings. A more electron-rich ring (p-methoxyphenyl) reacted substantially faster than a simple phenyl ring, which was, in turn, slightly more reactive vs a 4-carbomethoxyphenyl ring. Photoinduced di-π-methane rearrangement of the initial DA adducts gave rise to unusual isomeric polycyclic adducts.
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85
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Li K, Huertas M, Brant C, Chung-Davidson YW, Bussy U, Hoye TR, Li W. (+)- and (−)-Petromyroxols: Antipodal Tetrahydrofurandiols from Larval Sea Lamprey (Petromyzon marinus L.) That Elicit Enantioselective Olfactory Responses. Org Lett 2014; 17:286-9. [DOI: 10.1021/ol5033893] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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86
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Woods BP, Hoye TR. Differential scanning calorimetry (DSC) as a tool for probing the reactivity of polyynes relevant to hexadehydro-Diels-Alder (HDDA) cascades. Org Lett 2014; 16:6370-3. [PMID: 25470072 PMCID: PMC4275131 DOI: 10.1021/ol503162k] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
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The
differential scanning calorimetry (DSC) behavior of a number
of alkyne-rich compounds is described. The DSC trace for each compound
exhibits an exothermic event at a characteristic onset temperature.
For the tri- and tetraynes whose [4 + 2] HDDA reactivity in solution
has been determined, these onset temperatures show a strong correlation
with the cyclization activation energy. The studies reported here
exemplify how the data available through this operationally simple
analytical technique can give valuable insights into the thermal behavior
of small molecules.
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87
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Willoughby PH, Niu D, Wang T, Haj MK, Cramer CJ, Hoye TR. Mechanism of the reactions of alcohols with o-benzynes. J Am Chem Soc 2014; 136:13657-65. [PMID: 25232890 PMCID: PMC4183651 DOI: 10.1021/ja502595m] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
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We
have studied reactions of secondary and primary alcohols with
benzynes generated by the hexadehydro-Diels–Alder (HDDA) reaction.
These alcohols undergo competitive addition vs dihydrogen transfer
to produce aryl ethers vs reduced benzenoid products, respectively.
During the latter process, an equivalent amount of oxidized ketone
(or aldehyde) is formed. Using deuterium labeling studies, we determined
that (i) it is the carbinol C–H and adjacent O–H hydrogen
atoms that are transferred during this process and (ii) the mechanism
is consistent with a hydride-like transfer of the C–H. Substrates
bearing an internal trap attached to the reactive, HDDA-derived benzyne
intermediate were used to probe the kinetic order of the alcohol trapping
agent in the H2-transfer as well as in the alcohol addition
process. The H2-transfer reaction is first order in alcohol.
Our results are suggestive of a concerted H2-transfer process,
which is further supported by density functional theory (DFT) computational
studies and results of a kinetic isotope effect experiment. In contrast,
alcohol addition to the benzyne is second order in alcohol, a previously
unrecognized phenomenon. Additional DFT studies were used to further
probe the mechanistic aspects of the alcohol addition process.
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88
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Woods B, Baire B, Hoye TR. Rates of hexadehydro-Diels-Alder (HDDA) cyclizations: impact of the linker structure. Org Lett 2014; 16:4578-81. [PMID: 25153729 PMCID: PMC4156263 DOI: 10.1021/ol502131r] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2014] [Indexed: 12/31/2022]
Abstract
The rates of the hexadehydro-Diels-Alder (HDDA) reaction of substrates containing, minimally, a 1,3,8-triyne subunit are reported. Several series of related substrates, differing in the nature of the three-atom tether that links the 1,3-diyne and diynophile, were examined. Seemingly small changes in substrate structure result in large differences in cyclization rate, spanning more than 8 orders of magnitude. The reactivity trends revealed by these studies should prove useful in guiding substrate design and choice of reaction conditions in future applications.
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89
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Bolton JM, Hillmyer MA, Hoye TR. Sustainable Thermoplastic Elastomers from Terpene-Derived Monomers. ACS Macro Lett 2014; 3:717-720. [PMID: 35590688 DOI: 10.1021/mz500339h] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
ABA triblock polymers were prepared by living anionic polymerization of the pinene-derivable monomers α-methyl-p-methylstyrene and myrcene. The resulting thermoplastic elastomers displayed microphase separation at moderate molar mass, an upper service temperature about 70 °C higher than traditional petroleum-derived styrenic thermoplastic elastomers, competitive tensile strengths of up to 10 MPa, impressive ultimate elongations of up to 1300%, and remarkably low energy loss recovery attributes.
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90
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Hassig CA, Zeng FY, Kung P, Kiankarimi M, Kim S, Diaz PW, Zhai D, Welsh K, Morshedian S, Su Y, O'Keefe B, Newman DJ, Rusman Y, Kaur H, Salomon CE, Brown SG, Baire B, Michel AR, Hoye TR, Francis S, Georg GI, Walters MA, Divlianska DB, Roth GP, Wright AE, Reed JC. Ultra-High-Throughput Screening of Natural Product Extracts to Identify Proapoptotic Inhibitors of Bcl-2 Family Proteins. ACTA ACUST UNITED AC 2014; 19:1201-11. [PMID: 24870016 DOI: 10.1177/1087057114536227] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Accepted: 04/26/2014] [Indexed: 12/30/2022]
Abstract
Antiapoptotic Bcl-2 family proteins are validated cancer targets composed of six related proteins. From a drug discovery perspective, these are challenging targets that exert their cellular functions through protein-protein interactions (PPIs). Although several isoform-selective inhibitors have been developed using structure-based design or high-throughput screening (HTS) of synthetic chemical libraries, no large-scale screen of natural product collections has been reported. A competitive displacement fluorescence polarization (FP) screen of nearly 150,000 natural product extracts was conducted against all six antiapoptotic Bcl-2 family proteins using fluorochrome-conjugated peptide ligands that mimic functionally relevant PPIs. The screens were conducted in 1536-well format and displayed satisfactory overall HTS statistics, with Z'-factor values ranging from 0.72 to 0.83 and a hit confirmation rate between 16% and 64%. Confirmed active extracts were orthogonally tested in a luminescent assay for caspase-3/7 activation in tumor cells. Active extracts were resupplied, and effort toward the isolation of pure active components was initiated through iterative bioassay-guided fractionation. Several previously described altertoxins were isolated from a microbial source, and the pure compounds demonstrate activity in both Bcl-2 FP and caspase cellular assays. The studies demonstrate the feasibility of ultra-high-throughput screening using natural product sources and highlight some of the challenges associated with this approach.
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91
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Wohl AR, Michel AR, Kalscheuer S, Macosko CW, Panyam J, Hoye TR. Silicate esters of paclitaxel and docetaxel: synthesis, hydrophobicity, hydrolytic stability, cytotoxicity, and prodrug potential. J Med Chem 2014; 57:2368-79. [PMID: 24564494 PMCID: PMC3983351 DOI: 10.1021/jm401708f] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
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We report here the synthesis and
selected properties of various
silicate ester derivatives (tetraalkoxysilanes) of the taxanes paclitaxel
(PTX) and docetaxel (DTX) [i.e., PTX-OSi(OR)3 and DTX-OSi(OR)3]. Both the hydrophobicity and hydrolytic lability of these
silicates can be (independently) controlled by choice of the alkyl
group (R). The synthesis, structural characterization, hydrolytic
reactivity, and in vitro cytotoxicity
against the MDA-MB-231 breast cancer cell line of most of these derivatives
are described. We envision that the greater hydrophobicity of these
silicates (vis-à-vis PTX or DTX itself) should be advantageous
from the perspective of preparation of stable aqueous dispersions
of amphiphilic block-copolymer-based nanoparticle formulations.
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92
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Marell DJ, Emond SJ, Kulshrestha A, Hoye TR. Analysis of seven-membered lactones by computational NMR methods: proton NMR chemical shift data are more discriminating than carbon. J Org Chem 2014; 79:752-8. [PMID: 24354614 DOI: 10.1021/jo402627s] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We report an NMR chemical shift study of conformationally challenging seven-membered lactones (1-11); computed and experimental data sets are compared. The computations involved full conformational analysis of each lactone, Boltzmann-weighted averaging of the chemical shifts across all conformers, and linear correction of the computed chemical shifts. DFT geometry optimizations [M06-2X/6-31+G(d,p)] and GIAO NMR chemical shift calculations [B3LYP/6-311+G(2d,p)] provided the computed chemical shifts. The corrected mean absolute error (CMAE), the average of the differences between the computed and experimental chemical shifts for each of the 11 lactones, is encouragingly small (0.02-0.08 ppm for (1)H or 0.8-2.2 ppm for (13)C). Three pairs of cis versus trans diastereomeric lactones were used to assess the ability of the method to distinguish between stereoisomers. The experimental shifts were compared with the computed shifts for each of the two possible isomers. We introduce the use of a "match ratio"--the ratio of the larger CMAE (worse fit) to the smaller CMAE (better fit). A greater match ratio value indicates better distinguishing ability. The match ratios are larger for proton data [2.4-4.0 (av = 3.2)] than for carbon [1.1-2.3 (av = 1.6)], indicating that the former provide a better basis for discriminating these diastereomers.
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93
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Hoye TR, Baire B, Wang T. Tactics for Probing Aryne Reactivity: Mechanistic Studies of Silicon-oxygen Bond Cleavage During the Trapping of (HDDA-generated) Benzynes by Silyl Ethers. Chem Sci 2014; 5:545-550. [PMID: 25419449 DOI: 10.1039/c3sc53014k] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We report mechanistic aspects of the trapping of thermally (HDDA) generated benzyne derivatives by pendant silyl ether groups, which results in net insertion of the pair of benzyne Csp-hydribized carbon atoms into the silicon-oxygen sigma bond. Cross-over experiments using symmetrical, doubly labeled bis-silyl ether substrates established that the reaction is unimolecular in nature. Competition experiments involving either intramolecular or intermolecular dihydrogen transfer clock reactions (from within a TIPS isopropyl group or cyclooctane, respectively) vs. the silyl ether cyclization were used to gain additional insights. We evaluated effects of the steric bulk of the silyl ether trapping group and of the ring-size of the cyclic ether being formed (furan vs. pyran). These types of competition experiments allow the relative rates of various product-determining steps to be determined. This previously has only rarely been possible because aryne formation is typically rate-limiting, making it challenging to probe the kinetics of subsequent trapping reactions. Solvent effects (polarity of the medium) and computational studies were used to probe the question of stepwise vs. concerted pathways for the Si-O insertion.
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94
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Chen J, Baire B, Hoye TR. CYCLOADDITION REACTIONS OF AZIDE, FURAN, AND PYRROLE UNITS WITH BENZYNES GENERATED BY THE HEXADEHYDRO-DIELS-ALDER (HDDA) REACTION. HETEROCYCLES 2014; 88:1191-1200. [PMID: 24910496 DOI: 10.3987/com-13-s(s)83] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Benzynes can be generated by the intramolecular thermal cycloisomerization of triynes-the title HDDA reaction. We report here that these can be trapped by cycloaddition reaction with trimethylsilyl azide (1,3-dipolar) or a furan or pyrrole (4+2 Diels-Alder).
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95
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Niu D, Wang T, Woods BP, Hoye TR. Dichlorination of (hexadehydro-Diels-Alder generated) benzynes and a protocol for interrogating the kinetic order of bimolecular aryne trapping reactions. Org Lett 2013; 16:254-7. [PMID: 24329102 DOI: 10.1021/ol403258c] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The efficient dichlorination of benzynes prepared by the hexadehydro-Diels-Alder (HDDA) reaction is reported. Cycloisomerization of a triyne substrate in the presence of dilithium tetrachlorocuprate is shown to provide dichlorinated products A by capture of the benzyne intermediate. A general strategy for discerning the kinetic order of an external aryne trapping agent is presented. It merely requires measurement of the competition between bimolecular vs unimolecular trapping events (here, dichlorination vs intramolecular Diels-Alder (IMDA) reaction to give A vs B, respectively) as a function of the concentration of the trapping agent.
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96
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Pustulka KM, Wohl AR, Lee HS, Michel AR, Han J, Hoye TR, McCormick AV, Panyam J, Macosko CW. Flash nanoprecipitation: particle structure and stability. Mol Pharm 2013; 10:4367-77. [PMID: 24053447 PMCID: PMC3946569 DOI: 10.1021/mp400337f] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Flash nanoprecipitation (FNP) is a process that, through rapid mixing, stabilizes an insoluble low molecular weight compound in a nanosized, polymer-stabilized delivery vehicle. The polymeric components are typically amphiphilic diblock copolymers (BCPs). In order to fully exploit the potential of FNP, factors affecting particle structure, size, and stability must be understood. Here we show that polymer type, hydrophobicity and crystallinity of the small molecule, and small molecule loading levels all affect particle size and stability. Of the four block copolymers (BCP) that we have studied here, poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) (PEG-b-PLGA) was most suitable for potential drug delivery applications due to its ability to give rise to stable nanoparticles, its biocompatibility, and its degradability. We found little difference in particle size when using PLGA block sizes over the range of 5 to 15 kDa. The choice of hydrophobic small molecule was important, as molecules with a calculated water-octanol partition coefficient (clogP) below 6 gave rise to particles that were unstable and underwent rapid Ostwald ripening. Studies probing the internal structure of nanoparticles were also performed. Analysis of differential scanning calorimetry (DSC), cryogenic transmission electron microscopy (cryo-TEM), and (1)H NMR experiments support a three-layer core-shell-corona nanoparticle structure.
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97
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Dings RPM, Levine JI, Brown SG, Astorgues-Xerri L, MacDonald JR, Hoye TR, Raymond E, Mayo KH. Polycationic calixarene PTX013, a potent cytotoxic agent against tumors and drug resistant cancer. Invest New Drugs 2013; 31:1142-50. [PMID: 23392775 PMCID: PMC4242102 DOI: 10.1007/s10637-013-9932-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Accepted: 01/24/2013] [Indexed: 01/01/2023]
Abstract
Previously, we reported on the anti-tumor activities of two designed calix[4]arene-based topomimetics (PTX008 and PTX009) of the amphipathic, angiostatic peptide Anginex. Here, we chemically modified the hydrophobic and hydrophilic faces of PTX008 and PTX009, and discovered new calixarene compounds that are more potent, cytotoxic anti-tumor agents. One of them, PTX013, is particularly effective at inhibiting the growth of several human cancer cell lines, as well as drug resistant cancer cells. Mechanistically, PTX013 induces cell cycle arrest in sub-G1 and G0/G1 phases of e.g. SQ20B cells, a radio-resistant human head and neck carcinoma model. In the syngeneic B16F10 melanoma tumor mouse model, PTX013 (0.5 mg/Kg) inhibits tumor growth by about 50-fold better than parent PTX008. A preliminary pharmacodynamics study strongly suggests that PTX013 exhibits good in vivo exposure and a relatively long half-life. Overall, this research contributes to the discovery of novel therapeutics as potentially useful agents against cancer in the clinic.
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98
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Hoye TR, Ayyad SEN, Beckord HJ, Brown SG. New Diarylheptanoids and a Hydroxylated Ottelione from Ottelia alismoides. Nat Prod Commun 2013. [DOI: 10.1177/1934578x1300800320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Ten new diarylheptanoids (2, 3, 4, 5a-d, 6, 7, and 8) have been isolated from an extract of Ottelia alismoides. The structures of these previously unknown metabolites were determined by NMR spectroscopic analysis. A previously unknown, hydroxylated analog of the known otteliones A and B (1a and 1b)–namely, 3a-hydroxyottelione (13)–was also isolated. The 1H NMR analysis of the Mosher esters of alcohols derived from otteliones A and B (S-17/R-17 and S-20/R-20) are also reported.
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99
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Hoye TR, Ayyad SEN, Beckord HJ, Brown SG. New diarylheptanoids and a hydroxylated ottelione from Ottelia alismoides. Nat Prod Commun 2013; 8:351-358. [PMID: 23678810 PMCID: PMC4726472] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/02/2023] Open
Abstract
Ten new diarylheptanoids (2, 3, 4, 5a-d, 6, 7, and 8) have been isolated from an extract of Ottelia alismoides. The structures of these previously unknown metabolites were determined by NMR spectroscopic analysis. A previously unknown, hydroxylated analog of the known otteliones A and B (1a and 1b)--namely, 3a-hydroxyottelione (13)--was also isolated. The 1H NMR analysis of the Mosher esters of alcohols derived from otteliones A and B (S-17/R-17 and S-20/R-20) are also reported.
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100
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Baire B, Niu D, Willoughby PH, Woods BP, Hoye TR. Synthesis of complex benzenoids via the intermediate generation of o-benzynes through the hexadehydro-Diels-Alder reaction. Nat Protoc 2013; 8:501-8. [PMID: 23411632 DOI: 10.1038/nprot.2013.017] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The hexadehydro-Diels-Alder (HDDA) cascade enables the synthesis of complex benzenoid products with various substitution patterns through aryne intermediates. The first stage of this cascade involves the generation of a highly reactive ortho-benzyne intermediate by a net [4+2] cycloisomerization of a triyne substrate. The benzyne can be rapidly 'trapped' either intramolecularly or intermolecularly with myriad nucleophilic or π-bond-donating reactants. As a representative example of a general procedure for synthesizing highly substituted benzenoids, this protocol describes the synthesis of a typical triyne substrate and its use as the reactant in an HDDA cascade to form a phthalide. The synthetic procedure detailed herein (four chemical reactions) takes 16-20 h of active effort over a period of several days for the preparation of the triyne precursor and ∼2 h of active effort over a 3-d period for the generation and trapping of the benzyne and isolation of the phthalide product.
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