Improved synthesis of structural analogues of (−)-epicatechin gallate for modulation of staphylococcal β-lactam resistance

The high-yielding synthesis of enantiomerically pure epicatechin gallate analogues where the A and/or B-ring hydroxylation is reduced or altered has been achieved by optimising routes to the catechin stereochemistry. The B-ring analogues were synthesised by using an electrophilic ring closure onto an enantiomerically enriched epoxide as a key step. The A and B-ring hydroxyl-deleted analogues were synthesised through a Mitsunobu cyclisation. For the B-ring analogues, the anti- (catechin) stereochemistry was converted to the syn- (epicatechin) stereochemistry by a known oxidation/reduction protocol. Absolute stereochemistry was derived from either a Sharpless epoxidation or asymmetric dihydroxylation.     

Asymmetric synthesis of (−)-(R)-sitagliptin

The asymmetric synthesis of (?)-(R)-sitagliptin was achieved in seven steps from commercially available starting materials using the highly diastereoselective conjugate additions of either lithium (R)-N-benzyl-N-(α-methylbenzyl)amide or lithium (R)-N-benzyl-N-(α-methyl-p-methoxybenzyl)amide to tert-butyl 4-(2′,4′,5′-trifluorophenyl)but-2-enoate to install the correct stereochemistry. Subsequent sequential acid-catalysed hydrolysis of the resultant β-amino esters, HOBt/EDC mediated coupling with the triazolopyrazine fragment, and hydrogenolysis gave (?)-(R)-sitagliptin in 43% and 42% overall yields, respectively.     

Asymmetric synthesis of (−)-(1R,7aS)-absouline

The most efficient and concise asymmetric synthesis of (?)-(1R,7aS)-absouline to date, which was accomplished in eight steps and 20% overall yield from commercially available starting materials, is described. The doubly diastereoselective conjugate addition of lithium (S)-N-benzyl-N-(α-methylbenzyl)-amide to an enantiopure α,β-unsaturated ester derived from l-proline was employed as the key step. Subsequent hydrogenolytic N-debenzylation and acid-promoted cyclisation of the resultant β-amino ester produced the 1-aminopyrrolizidin-3-one scaffold, then reduction with DIBAL-H was followed by DCC-mediated coupling with (E)-p-methoxycinnamic acid to complete the synthesis of (?)-(1R,7aS)-absouline.     

An efficient synthesis of (R)-(−)-baclofen

In this report we describe an efficient synthesis of (R)-(−)-baclofen, a selective GABA_B agonist used as an antispastic agent. Our strategy is based on an enantioselective deprotonation of a cyclobutanone easily obtained by [2+2] cycloaddition of 4-chlorostyrene and dichloroketene.     

Total synthesis of (−) verbenalol and (−) epiverbenalol

The first asymmetric synthesis of (−) verbenalol and (−) epiverbenalol, starting from the organometallic complex (−) 1, is described.     

Total synthesis of (−)-lentiginosine

A simple and practical synthesis of (−)-lentiginosine 2 with good overall yield has been achieved from the commercially available diethyl d-tartarate. The key steps are a highly stereoselective Grignard reaction on an aldehyde and a Staudinger reduction.     

Stereoselective synthesis of (−)-cytoxazone

A novel stereoselective synthesis of (−)-cytoxazone 1 was achieved via addition of p-methoxyphenylmagnesium bromide to the benzylimine derived from (S)-2,3-O-isopropylidene glyceraldehyde followed by one-step regioselective cyclization of N-Boc amino diol 7.     

Total synthesis of (−)-vindoline

In this full paper, a stereocontrolled strategy for the total synthesis of (?)-vindoline is described. This synthetic route features: 1) rapid construction of the stereochemical center at C19 through a highly diastereoselective vinylogous Mannich addition; 2) tandem Heathcock/aza-Prins cyclization to install rings C and E in vindoline; 3) oxidative transformation of β-ketoester to enone; 4) stereoselective inversion of C4 stereochemistry with triphenylphosphine and carbon tetrabromide followed by Brønsted acid.     

The synthesis of (−)-cis- and (−)-trans-crobarbatic acid

The synthesis of both cis- and trans-crobarbatic acid is reported. The five-step sequence proceeds in high yield and with control of both relative and absolute stereochemistry. The key step in the synthesis is the Birch reductive alkylation of a chiral furoic acid which sets the absolute stereochemistry of the products. The stereochemistry of the compounds described was proven unambiguously by X-ray crystallography on one synthetic intermediate and on trans-crobarbatic acid.     

Convergent total synthesis of (−)-dactylolide

A convergent total synthesis of (?)-dactylolide is described. Constructing the 2,6-disubstituted exo-methylene THP moiety was achieved by the intramolecular allylation of α-acetoxy ether. The cyclization precursor was prepared from two segments, an alcohol and carboxylic acid derivatives, by esterification followed by reductive acetylation.     

A novel synthesis of (−)-callicarpenal

Callicarpenal, isolated from the leaves of American beautyberry (Callicarpa americana) and Japanese beautyberry (Callicarpa japonica), exhibits significant mosquito bite-deterring activity and repellent activity against ticks and fire ants. The mosquito bite-deterring activity level of callicarpenal was reported to be similar to that of N,N-diethyl-m-toluamide. The novel synthesis of (?)-callicarpenal reported herein was accomplished by starting from (+)-pulegone. In our original approach, a novel Prins-type cyclization based on Meyer–Schuster rearrangement was featured as a key step.     

First total synthesis of (−)-salprzelactone

The first enantioselective total synthesis of (?)-salprzelactone, a seco-norabietane diterpenoid has been accomplished in only three steps. Key transformations of the synthesis include an intermolecular aldol reaction and lactonization.     

A simple synthesis of (−)-(R)-ipsdienol and (−)-(S)-ipsenol

A short and efficient synthesis of the unnatural enantiomer of (+)-(S)-ipsdienol 1 and (−)-(S)-ipsenol 2 is presented via an asymmetric allylboration. The synthesis was achieved by using a one-pot reduction–methylenation of an exo-methylene lactone intermediate.     

Enantioselective synthesis of (−)-γ-jasmolactone

The title compound was prepared in seven steps starting from the commercially available 4-ketopimelic acid. The key step features an enantioselective lactonization promoted by PPL.     

The total synthesis of (−)-indolactam I

The first total synthesis of (−)-indolactam I (1) is reported. An efficient synthetic route was established to furnish the natural product in 8 steps. This strategy employed a copper-catalyzed amino acid arylation, peptide coupling, and Lewis acid-mediated macrocyclization to yield 1 from readily available building blocks. In addition, the cell growth inhibition activity of the natural product was examined through assays with the K562 leukemia cell line.     

First total synthesis of (−)-aplyolide A

The first total synthesis of (−)-aplyolide A², (16S)-methyloxacyclohexadeca-(5Z,8Z,11Z,14Z)-tetraen-2-one, 1 is reported. The synthesis is based on three consecutive couplings of terminal alkynes with propargylic halides and proves the absolute configuration of the stereogenic center of the natural product.     

An expeditious formal synthesis of (−)-epibatidine

A short route to (−)-epibatidine is described. It includes a hetero-Diels–Alder reaction of a chiral non-racemic acyl-nitroso derivative and 2-t-butyldimethylsilyloxycyclohexadiene followed by chemical manipulations to furnish a known precursor of the natural product in 11% overall yield.     

Enantioselective synthesis of (R)-(−)-mevalonolactone via cyclic sulfate methodology

An asymmetric synthesis of (R)-(−)-mevalonolactone is described using the Sharpless asymmetric dihydroxylation and the regioselective nucleophilic opening of a cyclic sulfate as key steps.     

Asymmetric synthesis of (R)-(−)-chlozolinate through a chemoenzymatic procedure

A new asymmetric synthesis of (R)-chlozolinate 1, an important antifungal agent, based on the enzymatic asymmetrization of diethyl 2-benzyloxy-2-methylmalonate, is reported.     

Enantioselective synthesis of herbertane sesquiterpenes: synthesis of (−)-α-formylherbertenol

The synthesis of 4-hydroxy-3-[(1S)-1,2,2-trimethylcyclopentyl]benzaldehyde [(−)-α-formylherbertenol 1], a herbertane-type sesquiterpene isolated from the leafy liverwort Herberta adunca, from β-cyclogeraniol is described. The synthesis is based on the previously described preparation of an enantiopure 1,2,2-trimethylcyclopentane synthon from which the characteristic aromatic moiety of 1 is elaborated, using a Robinson annulation and a palladium-catalysed methoxycarbonylation of an aryl triflate as key synthetic steps. The synthesis of the natural sesquiterpene (−)-α-herbertenol, also a natural sequiterpene, using the same methodology is also described.