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At least 1,351 records · Page 75Linked to original sources
PubMed2002

Pyranmycins, a novel class of aminoglycosides with improved acid stability: the SAR of D-pyranoses on ring III of pyranmycin.

[reaction: see text] The synthesis of a novel class of aminoglycosides, pyranmycins, is reported along with the structure activity relationship (SAR) of their antibacterial activity against Escherichia coli. Two pyranmycins show prominent activity (9 microM). Pyranmycins also manifest superior stability in acidic media. The SAR information will lead to the future designs of pyranmycin against drug resistant bacteria.

Aminoglycosides↗
PubMed2003

1,6-asymmetric induction in boron-mediated aldol reactions: application to a practical total synthesis of (+)-discodermolide.

By relying solely on substrate-based stereocontrol, a practical total synthesis of the microtubule-stabilizing anticancer agent (+)-discodermolide has been realized. This exploits a novel aldol bond construction with 1,6-stereoinduction from the boron enolate of (Z)-enone 3 in addition to aldehyde 2. The 1,3-diol 7 is employed as a common building block for the C(1)-C(5), C(9)-C(16), and C(17)-C(24) subunits. [reaction--see text]

Alkanes↗
PubMed2003

Total synthesis of (-)-pironetin.

[structure: see text] The asymmetric total synthesis of pironetin, a compound that shows plant growth regulatory activity, immunosuppressive as well as a remarkable antitumoral activity, is described. The approach involves the use of three very efficient Evans oxazolidinone-mediated syn-aldol condensations, a high-yielding coupling between lithium acetylide ethylenediamine complex and a tosylate followed by methylation, and selective reduction to establish the C12-C13 (E) double bond.

Molecular Structure↗
PubMed2003

Catalytic asymmetric synthesis of both syn- and anti-3,5-dihydroxy esters: application to 1,3-polyol/alpha-pyrone natural product synthesis.

[reaction: see text] We describe a catalytic asymmetric synthesis of both syn- and anti-3,5-dihydroxy esters. The method relies upon catalytic asymmetric epoxidation of alpha,beta-unsaturated imidazolides and amides, using lanthanide-BINOL complexes, and diastereoselective reduction of ketones. The method was applied to the enantioselective syntheses of 1,3-polyol/alpha-pyrone natural products 9a, 9b, and strictifolione (10). The absolute stereochemistry of 9a and 9b was also determined.

Biological Factors↗
PubMed2003

Enzymatic formation of unnatural novel polyketides from alternate starter and nonphysiological extension substrate by chalcone synthase.

[reaction: see text] In the chalcone synthase (CHS) enzyme reaction, both the starter molecule and the extension unit of the polyketide chain elongation reaction were simultaneously replaced with nonphysiological substrates. When incubated with benzoyl-CoA and methylmalonyl-CoA as substrates, recombinant CHS from Scutellaria baicalensis afforded an unnatural novel triketide, 4-hydroxy-3,5-dimethyl-6-phenyl-pyran-2-one, along with a tetraketide, 4-hydroxy-3,5-dimethyl-6-(1-methyl-2-oxo-2-phenyl-ethyl)-pyran-2-one. On the other hand, the enzyme also accepted hexanoyl-CoA and methylmalonyl-CoA as substrates to produce an unnatural novel triketide, 4-hydroxy-3,5-dimethyl-6-pentyl-pyran-2-one.

Acyl Coenzyme A↗
PubMed2003

Novel antiinsectan oxalicine alkaloids from two undescribed fungicolous Penicillium spp.

15-Deoxyoxalicine B (1) and decaturins A (2) and B (3) have been isolated from Penicillium decaturense and Penicillium thiersii, two previously undescribed species obtained as colonists of wood-decay fungi. The structures were determined by 2D NMR experiments and/or single-crystal X-ray diffraction analysis. These compounds are members of a rare structural class, and decaturins A and B feature a new polycyclic ring system. Decaturin B (3) exhibited potent antiinsectan activity against the fall armyworm (Spodoptera frugiperda).

Alkaloids↗
PubMed2003

On the structure of passifloricin A: asymmetric synthesis of the delta-lactones of (2Z,5S,7R,9S,11S)- and (2Z,5R,7R,9S,11S)tetrahydroxyhexacos-2-enoic acid.

Stereoselective syntheses of the delta-lactone of (2Z,5S,7R,9S,11S)-tetrahydroxyhexacos-2-enoic acid, the structure reported for passifloricin A, and of its (5R)-epimer are described. The creation of all stereogenic centers relied upon Brown's asymmetric allylation methodology. The lactone ring was created via ring-closing metathesis. The NMR data of both synthetic products, however, were different from those of the natural product. The published structure of passifloricin A is thus erroneous and will require further synthetic work to be unambiguously assigned. [structure: see text]

Cyclization↗
PubMed2003

Formal synthesis of (+)-discodermolide.

[structure: see text] Herein we report the formal total synthesis of (+)-discodermolide in 21 steps (longest linear sequence) from commercially available Roche ester. This synthesis features the assembly of C(9-18) and C(19-24) fragments via a metal-chelated aldol coupling reaction.

Alkanes↗
PubMed2003

Total synthesis of (-)- and (+)-membrenone C.

[reaction: see text] A synthesis of the polypropionate marine defense substance (+)-membrenone C and its enantiomer that starts from (S)-2-methyl-3-(tert-butyldimethylsilyloxy)propanal is described. Key steps include (1) additions of chiral allenylmetal reagents to effect both chain homologation and the concomitant introduction of four stereo centers, (2) a bis-intramolecular hydrosilylation-oxidation sequence to install beta-hydroxy ketone subunits, and (3) a bis-intramolecular aldol reaction to construct the two dihydropyrone termini.

Cyclization↗
PubMed2003

Enantioselective syntheses of cryptocarya triacetate, cryptocaryolone, and cryptocaryolone diacetate.

[reaction: see text] The enantioselective syntheses of three natural products from Cryptocarya latifolia have been achieved in 13-15 steps from ethyl sorbate. The route relies upon an enantio- and regioselective Sharpless dihydroxylation and a palladium-catalyzed reduction to establish the absolute stereochemistry. The route also relies upon a highly (E)-selective olefin cross-metathesis reaction to form trans-delta-hydroxy-1-enoates. The resulting delta-hydroxy-1-enoates were subsequently converted into cryptocarya triacetate, cryptocaryolone, and cryptocaryolone diacetate.

Acetates↗
PubMed2003

Total synthesis of (+)-strictifolione.

[reaction: see text] The synthesis of (+)-strictifolione was achieved from 3-phenylproprionaldehyde by using enantioselective allyltitanations to control the stereogenic centers at C6, C4', and C6' and a cross-methathesis to control the configuration of the double bond at C1'-C2'.

Aldehydes↗
PubMed2003

Synthesis of enantioenriched propargylic alcohols related to polyketide natural products. A comparison of methodologies.

[reaction: see text] Applications of methodology for the synthesis of propargylic alcohols related to polyketide natural products were examined. Noyori's asymmetric transfer hydrogenation of alpha-chiral alkynones was found to be highly selective and catalyst controlled. Additions of TMS acetylene to alpha-chiral aldehydes, catalyzed by a Ti(O-i-Pr)(4)-BINOL complex, were diastereoselective but substrate dependent.

Acetylene↗
PubMed2003

Synthesis of homoallylic chiral tertiary alcohols via chelation-controlled diastereoselective nucleophilic addition on alpha-alkoxyketones: application for the synthesis of the C(1)-C(11) subunit of 8-epi-fostriecin.

[reaction: see text] Chiral beta-syn-alkoxyhomoallylic alcohols derived from alkoxyallylboration of aldehydes upon oxidation provided the corresponding chiral ketones. Chelation-controlled nucleophilic addition to these ketones occurred in a highly stereoselective manner to afford anti-homoallylic tertiary alcohols. This methodology has been applied for the synthesis of the C(1)-C(11) subunit of C(8)-epi-fostriecin.

Alkenes↗