Letters in Organic Chemistry - Volume 2, Issue 3, 2005

The development of peptide-based enzyme mimics as organic catalysts for enantioselective synthesis is of rapidly growing interest today. In the following a brief overview about advantages of oligopeptide catalysts and recent achievements in peptide-catalyzed asymmetric synthesis, published in 2004, is given.

1-Ethenylcyclopropyl sulfonate underwent electrophilic γ- and α-substitutions by the carbonyls of naturally occurring biphenyls derived from vanillin and acetovanillone, in the presence of palladium(0) and diethylzinc, to provide regioisomeric 5,5'-di(3-cyclopropylidene-1-hydroxypropyl) biphenyls and 5,5'-di[1-(1-ethenylcyclopropyl)-1-hydroxymethyl]biphenyls of biological interest.

In the presence of catalytic amounts of Cp*RuCl(cod), the [2 + 2 + 2] cycloaddition of 1,6-diynes with ethynylferrocene proceeded at ambient temperature to afford ferrocenylbenzenes in 62-72% yields. An unsymmetrical 1,6-diyne bearing a ferrocenyl terminal was allowed to react with monoalkynes to give the corresponding meta-substituted cycloadducts selectively as single regioisomers. On the other hand, Bis(ferroce Read More

Methodology for preparation of the C8-C16 dienylamine segment of the streptogramin antibiotics is based on a diastereoselective nitrile oxide-olefin cycloaddition to a (triene)iron complex. The Fe(CO)3 adjunct also serves as a protecting group for the subsequent reductive hydrolysis of the isoxazoline ring.

The 3+2 cycloaddition reaction of nitrones and nitrile oxides with activated exo-glycals obtained from the Wittig reaction of sugar lactones gave good yields of only two cycloadducts. The reaction was efficiently carried out under microwave activation.

Hitherto unreported 3-(aryloxyacetyl)-2,3-dihydrothieno[3,2-c][1]benzothiopyran-4-ones (4a-f) were synthesized in excellent yield by the application of the tandem [2,3] and [3,3] sigmatropic rearrangements of the 4-(4' -aryloxybut-2'-ynylthio)[1]benzothiopyran-2-ones (3a-f). The substrates (3a-f) were synthesized by phase transfer catalyzed alkylation of previously unreported 4-mercaptothiopyran-2-ones with different 1-aryloxy-4 Read More

A strongly improved, highly stereoselective synthesis of (S)-α-trifluoromethyl aspartic acid via addition of lithium malonate to a chiral sulfinimine of trifluoropyruvate is presented.

In this communication a convenient and novel method for the stereospecific synthesis of chiral tetrahydroquinoxaline, 2,3-dihydro-benzo[1,4]dioxin and 2,3-dihydro-naphtho[2,3-b][1,4]dioxin derivatives from anhydro sugars is described.

Several 1-C-alkyl-2,3,4,6-tetra-O-benzyl-α-D-glucopyranosides were stereoselectively synthesized in good yields by the reaction of the 1-C-alkyl-2,3,4,6-tetra-O-benzyl-?-D-glucopyranosyl acetates with alcohols in the presence of 5 mol% Sc(OTf)3. The nature of the alkyl groups at the anomeric centers of the glycosyl donors had almost no influence on the reactivity and stereoselectivity of this glycosidation.

Several carba- and C-fucopyranosides have been tested as inhibitors of recombinant α 1,6- Fucosyltransferase from Rhizobium sp. 1-(R)-amino-phenylmethyl C-fucopyranoside (7) with 4C1(L) conformation showed the highest inhibition (IC50 = 690 μM). Molecular modeling alloweded us to establish an structure/activity relationship for the carba- and C-fucopyranosides inhibition activity.

Compound 1, a double p-tert-butylcalix[4]arene with direct para-para linkage, was obtained by FeCl3- mediated oxidative coupling of 5,11,17-tri-p-tert-butyl-26,27,28-tribenzoyloxycalix[4]arene-25-ol (4) followed by alkaline hydrolysis. With respect to the de-tert-butylated counterpart 1a, a different reactivity of 1 was observed in the NaH-promoted propylation, which gave octapropyl double-cone atropisomer 6 with higher st Read More

Multi-carbon bearing hydrocarbon molecules such as PAHs and long-chain-alkanes were obtained in the reaction of dolomite with metallic sodium. Fischer-Tropsch synthesis under the condition of supercritical carbon dioxide was proposed for the formation of PAHs and long-chain-alkanes. This result might be helpful to understand the formation mechanism of diamond and other carbon-based materials in CO2-alkali metal syste Read More

Two new degraded terpenoids and an aromatic compound,as well as kaurene,methyl p - tolylbenzoate,methyl 4-hydroxy-2-hydroxymethylbenzoate,and 1-(2,6,6-trimethyl-4-oxo-2-cyclohexenyl)- 2(E)-buten-1-one,were isolated from Ternstroemia gymnanthera .

The preparation of amides in ionic liquids was explored using the Schotten-Baumann procedure,the Weinreb amidation of esters and the classical coupling reaction using EDC,HBTU or DMTMM as the coupling agents.In any case amides were obtained in comparable or better yields and with a simplified procedure than using conventional solvents.Moreover,the amides were directly reduced in the same flask to the correspondin Read More

2-Benzothiazolyl 1-thiofuranosides derivatives of L-arabino-,D-ribo-and D-xylofuranose were synthesized in good yield in a one-pot reaction by treatment of reducing monosaccharides with diphenyl phosphorochloridate and 2-mercaptobenzothiazol under phase-transfer conditions.Their ability to act as glycosyl donors was demonstrated.

The Z isomer of the new constrained analog of the anticancer drug octreotide,where L,L-cystine is replaced by 4,5-dehydro-L,L-diaminosuberic acid,was prepared by solid-phase ring-closing metathesis.NMR study ascertained that this molecule is conformationally very close to the parent octreotide and remains unaffected by the enzymatic pool of the human serum for more than 30 h.

A series of substituted 3-bromoisoxazoles were ring opened with either molybdenum hexacarbonyl or iron (II)chloride tetrahydrate to give β -ketonitriles in good yields.