Total synthesis of Phytophthora mating hormone α1

Total synthesis of Phytophthora mating hormone α1 (1) has been demonstrated. The required stereochemistries (methyl) are achieved by applying CuI-(S)-Tol-BINAP-catalyzed conjugate addition of Grignard reagents to α,β-unsaturated esters.     

Synthesis and spectroscopic analysis of a stereoisomer library of the phytophthora mating hormone α1 and derived bis-Mosher esters

Fluorous mixture synthesis provided all eight diastereomers of the phytophthora hormone α1 with the R configuration at C11 as individual samples after demixing and detagging. The library of all possible bis-Mosher esters (16) was then made by esterification. Complete sets of (1)H, (13)C, and (for the Mosher esters) (19)F NMR spectra were recorded, assigned, and compared with each other and with published spectra. Not all of the spectra are unique, and the (1)H NMR spectra of the Mosher esters provided the most information. The previous assignment of the natural sample as an "all-R" stereoisomer mixed with its 3S-epimer was confirmed.     

A modular approach to aryl-C-ribonucleosides via the allylic substitution and ring-closing metathesis sequence. a stereocontrolled synthesis of all four α-/β- and D-/L-C-nucleoside stereoisomers

Iridium(I)-catalyzed allylation of the enantiopure monoprotected copper(I) alkoxide, generated from (S)-5a, with the enantiopure allylic carbonates (R)-9a,b has been developed as the key step in a new approach to C-nucleoside analogues. The anomeric center was thus constructed via a stereocontrolled formation of the C-O rather than C-C bond with retention of configuration. The resulting bisallyl ethers 15a,b (≥90% de and >99% ee) were converted into C-ribosides 29a,b via the Ru-catalyzed ring-closing metathesis, followed by a diastereoselective dihydroxylation catalyzed by OsO(4) or RuO(4) and deprotection. Variation of the absolute configuration of the starting segments 5a and 9a,b allowed a stereocontrolled synthesis of all four α/β-D/L-combinations.     

Catalytic asymmetric synthesis of stereoisomers of 1-C-n-butyl-LABs for the SAR study of α-glucosidase inhibition

We achieved synthesis of seven stereoisomers of 1-C-n-butyl-L-iminofuranose derivatives using catalytic asymmetric alkylation and Negishi coupling as key reactions. The synthetic strategy based on these key reactions was quite useful, since both α- and β-iminofuranoses could be obtained by switching the chirality of the ligand employed for the AAA reaction. The common intermediates for α- and β-isomers were subjected to further manipulations to install a diol unit at C2 and C3 to give the desired stereoisomers of L-iminofuranose derivatives. We achieved the preparation of all stereoisomers of 1-C-n-butyl-L-iminofuranose derivatives, with the exception of β-lyxo type iminofuranose. It is noteworthy that a synthetic route for many stereoisomers of iminofuranose derivatives was developed. Unfortunately, none of the L-iminofuranoses obtained showed inhibitory activity against the α-glycosidases examined—e.g., maltase, sucrase, and isomaltase.     

Concise synthesis of two pentasaccharides corresponding to the α-chain oligosaccharides of Neisseria gonorrhoeae and Neisseria meningitidis

Two pentasaccharides containing a common tetrasaccharide (lacto-N-neotetraose) core, and d-galactosamine and N-acetyl neuraminic acid in the non-reducing ends, respectively, corresponding to the lipooligosaccharides of Neisseria gonorrhoeae and Neisseria meningitidis were synthesized in a very concise manner from a common trisaccharide derivative using minimum number of steps. Thioglycosides and glycosyl trichloroacetimidate have been used as glycosyl donors for glycosylations and yields were excellent in every step.     

Semi-preparative liquid-chromatographic separation of all four stereoisomers of α-bisabolol on tribenzoylcellulose

Summary A semi-preparative low-pressure liquid-chromatographic procedure using tribenzoylcellulose has been developed for the separation and isolation of the four -bisabolol stereoisomers. Stereochemical assignments were made by HPLC-polarimeter coupling and by using the authentical isomers. This method can be applied to the quality control of chamomile preparations, as it allows the detection of adulterations resulting from admixtures of synthetic -bisabolol. In addition, the isolation of all four -bisabolol stereoisomers from commercially available synthetic -bisabolol has been made possible.     

A concise synthesis of a β-lactamase inhibitor

MK-7655 (1) is a β-lactamase inhibitor in clinical trials as a combination therapy for the treatment of bacterial infection resistant to β-lactam antibiotics. Its unusual structural challenges have inspired a rapid synthesis featuring an iridium-catalyzed N-H insertion and a series of late stage transformations designed around the reactivity of the labile bicyclo[3.2.1]urea at the core of the target.     

A new concise stereoselective method for the preparation of a β-hydroxyfurfurylamine derivative and synthesis of 1-deoxyazasugar isomers

A new method to prepare a chiral building block, a β-hydroxyfurfurylamine derivative, is achieved and 1-deoxyazasugar isomers are synthesized.     

A chemoenzymatic approach to the synthesis of the stereoisomers of a β-adrenergic receptor antagonist

The four stereoisomers of Δ²-isoxazoline 2, a β-adrenergic receptor antagonist structurally related to Falintolol 1, were prepared by an enzyme-catalyzed kinetic resolution of the unsaturated secondary alcohol (±)-7 followed by its cycloaddition to pyruvonitrile oxide. Through this strategy, diastereomeric aminoalcohols (+)-2a/(−)-2b and (−)-2a/(+)-2b were obtained in 99 and 92% enantiomeric excess, respectively. The absolute configuration to the target compounds was assigned via chemical correlation to the enantiomers of epoxides 4a and 4b, whose stereochemistry had been previously established.     

A facile and efficient synthesis of fully substituted pyridin-2(1H)-ones from α-oxoketene-S,S-acetals

A facile and efficient synthesis of fully substituted pyridin-2(1H)-ones has been developed by the reaction of readily available α-oxoketene-S,S-acetals with malononitrile in the presence of sodium methoxide in methanol under reflux.     

Syntheses and lipophilicity measurement of N/N-terminus-1,1-dihydroperfluoroalkylated α-amino acids and small peptides

(1,1-Dihydroperfluoroalkyl)phenyliodonium N,N-bis(trifluoromethylsulfonyl)imides (4, n = 0-2) were synthesized and used to transfer the corresponding 1,1-dihydroperfluoroalkyl groups to the α-amino group of (l)tyrosine. The obtained N^α-2,2,2-trifluoroethylated (l)tyrosine (6, n = 0) was further used as the N-terminus in the solid phase peptide synthesis of leucine enkephalin analogue. The lipophilicity of the N^α-1,1-dihydroperfluoroalkylated (l)tyrosines (6, n = 0-2) and N-terminus-2,2,2-trifluoroethylated leucine enkephalin analogue (7), as well as the corresponding parent compounds, was measured.     

Iodine-mediated regioselective C2-amination of indoles and a concise total synthesis of (±)-folicanthine

Highly substituted 2-aminated indoles can be prepared in moderate to excellent yields by regioselective C2-amination of indoles promoted by iodine. As a key step in a concise synthesis of (±)-folicanthine, its core structure was easily obtained by one step cyclization-dimerization of substituted tryptophan in high yield on a gram scale.     

A concise synthesis of paucifloral F and related indanone analogues via palladium-catalyzed α-arylation

A concise approach to synthesize paucifloral F was developed via a stereoselective palladium-catalyzed α-arylation reaction. The approach has also been applied in the synthesis of indanone analogues of Paucifloral F.     

Carbocyclic α-amino acids: asymmetric synthesis of all four 1-amino-2-hydroxycyclohexanecarboxylic acids

Starting from racemic 2-methoxycyclohexanone and (S)- or (R)-1-phenylethylamine, respectively, the four stereoisomers of 1-amino-2-hydroxycyclohexanecarboxylic acid are obtained via an asymmetric Strecker synthesis with ee values ranging from 87 to 98%. Their stereochemistry is established by NMR methods and by X-ray analyses. Hydrogenolysis of a benzylic C–N bond by conc. sulphuric acid as well as cleavage of a methoxy ether by conc. HCl are two intriguing reactions which are observed within the five-step procedure described herein.     

Stereoselective α-galactofuranosylation and synthesis of di- and tetrasaccharide subunits of cell wall polysaccharides of Talaromyces flavus

Stereoselective α-galactofuranosylation employing 2′-carboxybenzyl glycosides as galactosyl donors has been established. The tetrabenzyl-protective group on the galactosyl donor was essential for the α-galactosylation of secondary alcohol acceptors. The present method was successfully applied to the synthesis of di- and tetrasaccharide subunits of cell wall polysaccharides of Talaromyces flavus.     

Diphenylparabanic acid as a synthon for the synthesis of α-diketones and α-ketocarboxylic acids

Diphenylparabanic acid was found to react with >2 equiv of organolithiums at -78 °C to effectively give the corresponding symmetrical α-diketones. However, upon treatment with 1 equiv of organolithium, the parabanic acid gave mainly 5-substituted 5-hydroxyimidazolidine-2,4-diones. On the other hand, Grignard reagents were less reactive toward the parabanic acid at low temperature, and selectively gave the corresponding 5-hydroxyimidazolidine-2,4-diones even if more than 1 equiv of the reagents was used. A tandem process in which the parabanic acid was first reacted with a Grignard reagent and then reacted in one-pot with an organolithium effectively gave the unsymmetrical α-diketone. 5-Substituted 5-hydroxyimidazolidine-2,4-diones were useful as versatile precursors for preparing α-ketocarboxylic acids as well as unsymmetrical α-diketones.     

Semmler–Wolff aromatisation: a concise route for the synthesis of 5-amino-quinazolines and 4-amino-indoles

A simple and efficient methodology for the synthesis of 5-amino-quinazolines and 4-amino-indoles via Semmler–Wolff aromatisation reaction has been carried out. The oximation of keto intermediates followed by Semmler–Wolff aromatisation using acetic anhydride and a catalytic amount of sodium iodide in xylene provided the desired quinazolines and indoles.     

Catalytic asymmetric amination of N-nonsubstituted α-alkoxycarbonyl amides: concise enantioselective synthesis of mycestericin F and G

In an attempt to explore the synthetic utility of a ternary asymmetric catalyst comprising La(NO₃)₃?6H₂O, amide‐based ligand (R)‐ L1 , and D ‐valine tert‐butyl ester H‐D ‐Val‐OtBu, we investigated a catalytic, asymmetric amination of functionalized N‐nonsubstituted α‐alkoxycarbonyl amides using di‐tert‐butyl azodicarboxylate as an electrophilic aminating reagent. A highly functionalized, cyclic N‐nonsubstituted α‐alkoxycarbonyl amide delivered the desired amination product in up to 96 % enantiometric excess, with the requisite functionalities of the polar heads of sphingosines with the appropriate stereochemical arrangement. The rapid asymmetric assembly of these functional groups allowed a concise enantioselective synthetic route to sphingosines to be established with a broad flexibility towards derivative synthesis. These studies have culminated in an efficient catalytic enantioselective total synthesis of immunosuppressive fungal metabolites mycestericin F ( 3 a ) and G ( 3 b ).     

The synthesis of fluorinated α-pyrans via fluorinated vinylcopper reagents

Fluorinated vinylcopper reagents were prepared in situ via reaction of fluorinated vinylbromides or iodides with cadmium or zinc powder followed by metathesis with Cu(I)Br. Hexafluoro-2-butyne was then added to the solution of the F-vinylcopper reagent which resulted in a stereospecific syn addition of the F-vinylcopper reagent to the alkyne to provide in situ the corresponding dienylcopper reagent. Subsequent acylation of the dienylcopper reagent gave a dienylketone, which spontaneously cyclized to the 2H-pyran. This methodology provides a useful one flask route to fluorinated 2H-pyrans.