Synthesis of the proposed structure of queenslandon

The proposed structure of the benzolactone queenslandon (6) was synthesized utilizing a triol containing building block prepared from d-ribose. While a ring-closing metathesis approach did not lead to the macrocycle, alkylation of a benzyl(phenyl)selane, elimination to generate the styrene double bond, followed by Mitsunobu macrolactonization proved to be successful. Spectral data suggest that the structure of queenslandon should be revised, probably to the C11 epimer.     

Synthesis of the proposed structure of feigrisolide C

[reaction: see text] Possible structures of feigrisolide C were synthesized via ring-closing olefin metathesis reaction of a diester derivative prepared from 8-epi-nonactic acid, but physical characteristics of the synthetic samples did not match with those of the natural sample of feigrisolide C.     

Synthesis of the proposed structure of phaeosphaeride A

The first total synthesis of the proposed structure of phaeosphaeride A has been achieved via six-membered-ring formation by means of an intramolecular vinyl-anion aldol reaction as the key step. This synthesis suggests a revised configurational assignment for phaeosphaeride A.     

Synthesis of nonactin and the proposed structure of trilactone

[reaction: see text] An efficient enantioselective route to nonactin using a novel beta-inversion of an Evans syn aldol to construct the THF ring is presented. Through total synthesis, the structure for trilactone proposed in the literature is shown likely to be incorrect.     

Synthesis of sesquiterpenoids of the drimane group from labdane diterpenoids

Data on the partial synthesis of enantiomerically pure sesquiterpenoids of the drimane group, including valuable biologically active natural compounds, from accessible labdane diterpenoids are surveyed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 896–913, May 1997.     

Synthesis of the proposed structure of plakevulin A: revised structure of plakevulin A

A total synthesis of the proposed structure of plakevulin A was accomplished. However, the NMR spectral data of the synthetic plakevulin A were not identical of those of the reported compound. We next converted the synthetic plakevulin A into 1-dihydrountenone A. The ¹H and ¹³C NMR spectral data of 1-dihydrountenone A were identical with those of reported plakevulin A except for the peaks derived from levulinic acid. Thus, we repurified sample of the natural product and confirmed that the natural sample contained 1-dihydrountenone A and levulinic acid in the ratio of one to one. We also found that not plakevulin A but 1-dihydountenone A possessed the inhibitory activity against mammalian DNA polymerases α and β.     

Synthesis and anticancer activity of the proposed structure of caldoramide,an N-peptidyltetramate from the cyanobacterium Caldora penicillata

The structure proposed in the literature for caldoramide, a formal pentapeptide metabolite of the marine cyanobacterium Caldora penicillata, was synthesised in 12 steps and 16% yield (longest linear sequence from isoleucine) following the strategy of a stepwise consecutive extension of an N-oligopeptidyl chain on a tetramate anchor. The synthetic product differed from the natural isolate in optical rotation, some NMR data, and cytotoxicities. Its antiproliferative effect on three human cancer cell lines was distinctly lower than that of related dolastatin 10 and belamide A.     

Synthesis of a new nitrogenated drimane derivative with antifungal activity

Drimane sesquiterpenes are highly valuable due to their strong biological activity. In this work, we report the enhanced antifungal activity of 11-guanidinodrimene, a new compound derived from drimenol. The binding of the guanidine group at the C-11 carbon increased the antifungal activity when tested against Candida albicans, one of the most commonly found human pathogens.     

Synthesis of combinatorial libraries based on terpenoid scaffolds

Triterpenoid-based scaffolds betulinic acid (1a) and ursolic acid (1b), have been used for the generation of combinatorial libraries in parallel format using solid phase organic synthesis method. These templates have the potential for the synthesis and amplification of triterpenoid-based compounds with one and two-point diversity. This has been demonstrated by the synthesis of two small libraries comprising 18 derivatives each of betulinic acid and ursolic acid with structural diversity at C-3 and C-28 positions. The primary screening of antimalarial activity of these libraries against P. falciparum in vitro led to the identification of four compounds with 5 fold increase in the activity compared to betulinic and ursolic acids.     

Synthesis of Schiff bases on the basis of the isosteviol terpenoid

The transformation of the carboxy and keto groups of the isosteviol (ent-16-ketobeyeran-19-oic acid) diterpenoid was used to synthesize its new nitrogen-containing derivatives, including Schiff bases by the C⁴ and C¹⁶ atoms of the isosteviol frame. The structure of the resulting compounds was established by X-ray diffraction.     

Synthesis of the proposed structure of mucoxin via regio- and stereoselective tetrahydrofuran ring-forming strategies

An enantioselective total synthesis of the proposed structure of mucoxin (1) is described. Mucoxin, an annonaceous acetogenin isolated from bioactive leaf extracts of Rollinia mucosa, is the first acetogenin containing a hydroxylated trisubstituted tetrahydrofuran (THF) ring. This natural product is a highly potent and specific antitumor agent against MCF-7 (breast carcinoma) cell lines (ED50 = 3.7 x 10(-3) microg/mL compared to adriamycin, ED50 = 1.0 x 10(-2) microg/mL). The total synthesis described herein features two regio- and stereoselective THF ring-forming reactions. The 2,3,5-trisubstituted THF portion (C13-C17) was accessed using a highly regioselective cyclization of a methylene-interrupted epoxydiol, and the 2,5-disubstituted THF ring (C8-C12) was conveniently assembled via a 1,2-n-triol cyclization strategy. The spectral data of the synthetic material and two of its diastereomers did not match the reported data for the natural product. On the basis of detailed spectroscopic analysis of the synthesized molecule, we reason that the spectral discrepancies are due to stereochemical misassignment of the natural product.     

Occurrence, biological activity and synthesis of drimane sesquiterpenoids

In this review the names, structures and occurrence of all new drimanes and rearranged drimanes which have been published between January 1990 and January 2003 have been collected. Subjects that have been treated are biosynthesis, analysis, biological activities, with special attention to cytotoxic activity and antifeedant and insecticidal activity and mode of action. An important part of the review deals with the synthesis of drimanes. This part has been subdivided into syntheses by transformation of natural products, syntheses starting from chiral compounds obtained by enzymatic resolution, syntheses by cationic polyolefin cyclizations, syntheses from trans-decalones, syntheses by radical cyclizations and syntheses by cycloaddition reactions. The review contains about 350 references.     

Synthesis of the unique angular tricyclic chromone structure proposed for aspergillitine, and its relationship with alkaloid TMC-120B

The synthesis of the tricyclic angular chromone structure originally assigned to aspergillitine is reported. The synthesis was achieved in 11 steps and 15% overall yield from 2,4-dihydroxypropiophenone, through the intermediacy of 2,3-dimethyl-7-hydroxychromen-4-one. Construction of the nitrogen-bearing heterocyclic ring entailed a Stille cross-coupling reaction with n-Bu(3)SnCH(2)CH=CH(2), followed by double bond isomerization, oximation of the chromone carbonyl, and a final microwave-assisted electrocyclization of the thus formed 6π-electron aza-triene system.     

Total synthesis of the proposed structure of xylarolide

A total synthesis of a proposed structure of xylarolide is described. The key features of the synthesis include Sharpless asymmetric reaction, Wittig olefination, Sharpless asymmetric dihydroxylation, Still-Gennari olefination and Yamaguchi lactonization. The differences in the spectroscopic data of the synthetic and natural product indicate a revision of the assigned structure.     

Total synthesis of the proposed structure of brevenal

Total synthesis of the proposed structure of brevenal, a natural marine polycyclic ether product, has been accomplished. The synthesis features (i) convergent synthesis of the pentacyclic polyether skeleton using our developed Suzuki-Miyaura coupling strategy and (ii) construction of the multi-substituted dienal side chain by CuTC-mediated Stille reaction. Comparison of the NMR data of the synthetic compound with those reported for the natural product revealed that the proposed structure of brevenal needs to be revised.     

Total synthesis of the proposed structure of macrocaffrine

A full account of the total synthesis of 18-demethyl-19-hydroxy-N_a-demethyl-N_b-methylsuaveoline (1), the structure assigned to macrocaffrine isolated from Rauwolfia caffra, is presented. The key steps involved are an intramolecular cycloaddition reaction of the oxazole-olefin 10 and a subsequent dehydration that generated the pentacyclic pyridine derivative 14. The spectral data and specific rotation of synthetic 1 were dissimilar to those reported for a natural sample, leaving the structure of this R. caffra alkaloid undefined.     

Synthesis, structure and reactions of an amidinate stabilised trigallane

The neutral trigallane R(3)Ga(3)I(2) was obtained in high yields by reaction of "GaI" with the moderately sterically demanding lithium N,N'-dicyclohexylneopentylamidinate. Its chemical reactions with N-lithio-2-propanimine, sodium superhydride and elemental iodine were investigated. RI-DFT calculations have been performed to confirm the bonding situation. All compounds are characterised by crystal structure analysis and NMR-spectroscopy.     

A new drimane from the heartwood of the Japanese yew, Taxus cuspidata

A new drimane sesquiterpenoid was isolated from the heartwood of the Japanese yew, Taxus cuspidata Sieb. et Zucc. Its structure was established as 1beta-acetoxyisodrimeninol (1beta-acetoxy-11,12-epoxy-7-drimen-11-ol, 1). This compound was gradually oxidized to give y-lactone (1beta-acetoxy-8-drimeno-11,12-lactone, 4).