Ethyl (benzothiazol-2-ylsulfonyl)acetate: a new reagent for the stereoselective synthesis of α,β-unsaturated esters from aldehydes

Highly Stereoselective Diels-Alder-Based Strategy for the Synthesis of 3-epi-Formicin A and 1-epi-Formicin B

The first enantioselective approach based on a highly stereoselective Diels-Alder reaction for the synthesis of 3-epi-formicin A and 1-epi-formicin B with rare N-acetylcysteamine-containing indenone thioesters is reported. The strategy utilizes a key Diels-Alder reaction to form the core hydrindane system with three contiguous stereocenters in very high levels of diastereo- and regioselectivity and one-pot oxidation/isomerization/dehydrogenation. The scope of this method was tested with different substrates to give cycloadducts in a highly diastereoselective manner.

One-Pot O2-Oxidation and the Horner-Wadsworth-Emmons Reaction of Primary Alcohols for the Synthesis of (Z)-α,β-Unsaturated Esters

We developed one-pot oxidation/olefination procedures of primary alcohols giving Z-α,β-unsaturated esters 3. TEMPO-(CuCl or CuBr₂)-(2,2'-bipyridine) (1:1:1) catalyzed O₂ oxidation of primary alcohols in the presence of Z-selective Horner-Wadsworth-Emmons reagent 1b and K₃PO₄ or NaH gave 3 with Z/E = 84:16 to 96:4 in high yields. A stepwise reaction was also developed. After TEMPO-CuBr₂-(2,2'-bipyridine)-K₃PO₄ (1:1:1:1) catalyzed O₂ oxidation of alcohols in MeCN, the resulting mixture was treated with a THF solution of 1b and t-BuOK at -78 °C to 0 °C, giving 3 with higher selectivity (Z/E = 91:9 to 99:1).

Selective C-H chalcogenation of thiazoles via thiazol-2-yl-phosphonium salts

Thiazoles and benzothiazoles undergo regioselective C2-H chalcogenation via the sequence of thiazole C2-functionalization with phosphines to produce phosphonium salts which in turn react with S- and Se-centered nucleophiles to give products of C2-H chalcogenation and allow for recovery of the starting phosphine. The atom economical sequence proceeds under mild conditions and features broad scope for both the nucleophiles (electron-rich, electron-poor, sterically hindered thiols) and the various substituted benzothiazoles. The access to the substituted medicinally relevant C2-thio benzothiazoles also enables stereoselectivity improvements in the modified Julia olefinations.

Bromoacetate Olefination Protocol for Norbixin and Julia-Kocienski Olefination for Its Ester Syntheses

A new olefination protocol utilizing ethyl bromoacetate was highlighted, in which magnesium enolate of the ester coupled with C₂₀ dialdehyde 6, and double eliminations of the protected hydroxyl groups and bromine atoms of the coupling bromohydrin product, efficiently produced norbixin 1 after concomitant hydrolysis of the ester. A new (C₇ + C₁₀ + C₇) disconnection approach was demonstrated for the synthesis of norbixin ethyl ester 2 by the Julia-Kocienski olefination of novel C₇ benzothiazolyl-sulfone 11 and C₁₀ 2,7-dimethyl-2,4,6-octatrienedial (12).

A Novel Convergent Synthesis of the Potent Antiglaucoma Agent Tafluprost

Tafluprost (AFP-168, 5) is a unique 15-deoxy-15,15-difluoro-16-phenoxy prostaglandin F₂α (PGF_2α) analog used as an efficacious ocular hypotensive agent in the treatment of glaucoma and ocular hypertension, as monotherapy, or as adjunctive therapy to β-blockers. A novel convergent synthesis of 5 was developed employing Julia–Lythgoe olefination of the structurally advanced prostaglandin phenylsulfone 16, also successfully applied for manufacturing of pharmaceutical grade latanoprost (2), travoprost (3) and bimatoprost (4), with an aldehyde ω-chain synthon 17. The use of the same prostaglandin phenylsulfone 16, as a starting material in parallel syntheses of all commercially available antiglaucoma PGF_2α analogs 2–5, significantly reduces manufacturing costs resulting from its synthesis on an industrial scale and development of technological documentation. Another key aspect of the route developed is deoxydifluorination of a trans-13,14-en-15-one 30 with Deoxo-Fluor. Subsequent hydrolysis of protecting groups and final esterification of acid 6 yielded tafluprost (5). The main advantages are the preparation of high purity tafluprost (5) and the application of comparatively cheap reagents. The preparation and identification of two other tafluprost acid derivatives, tafluprost methyl ester (32) and tafluprost ethyl amide (33), are also described.

New fluorinated fructose analogs as selective probes of the hexose transporter protein GLUT5

Two fluorinated fructose analogs are taken up by tumor cells in culture. Their high affinity for the transporter protein GLUT5 provides information on the structural demands of its binding site, and suggests approaches towards new molecular imaging probes.

Use of Ethyl (Benzothiazol-2-ylsulfonyl)acetate for Malonic Ester-type Syntheses of Carboxylic Acids and Esters

A new methodology for the synthesis of substituted carboxylic acids is described. Alkylation of either ethyl (benzothiazol-2-ylsulfonyl)acetate or ethyl 2-(benzothiazol-2-ylsulfonyl)propionate was achieved with alkyl halides and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in dichloromethane solution. These products were then desulfinated and hydrolysed in one-pot under mild conditions to give substituted acetic acids in good-to-excellent yields.

Therapeutic uses of prostaglandin F(2α) analogues in ocular disease and novel synthetic strategies

The pharmacological management of glaucoma and ocular hypertension has significantly changed over the last 18 years with the introduction of PGF2α analogues, more specifically latanoprost (6), travoprost (8), bimatoprost (10) and tafluprost (12). Prostanoids are currently the first-line medicines among ocular antihypertensive drugs in terms of efficacy, safety, patient compliance and medical economy. Their ability to effectively reduce intraocular pressure with once-per-day dosing, ocular tolerability comparable to timolol and general lack of systemic adverse effects have made them the mainstay of pharmacological therapy for glaucoma and ocular hypertension all over the world. The present review reports a novel, convergent and highly diastereoselective method for the synthesis of PGF2α analogues from the structurally advanced prostaglandin phenylsulfone (5Z)-(+)-15 and new ω-chain synthons. The biochemistry, clinical efficacy and side effects of four commercially available PGF2α analogues, currently used as first-line agents for reducing intraocular pressure in patients with glaucoma or ocular hypertension, are also discussed.

Ligand-free Suzuki coupling of arylboronic acids with methyl (E)-4-bromobut-2-enoate: synthesis of unconventional cores of HIV-1 protease inhibitors

An effective ligand-free Suzuki coupling protocol to unite methyl (E)-4-bromobut-2-enoate with several arylboronic acids has been accomplished. Thus, a number of variously functionalized methyl 4-arylcrotonates have been achieved in high to excellent yields under mild conditions. This method enables the preparation of diverse aryl-substituted cores of HIV-1 protease inhibitors.

Practical synthesis of β-oxo benzo[d]thiazolyl sulfones: scope and limitations

In this paper, we discuss our new synthetic approach towards functionalized benzo[d]thiazolyl (BT) sulfones, based on the reunion of alkyl BT sulfones and various electrophiles (e.g. R-CO-X, RO-CO-X, RS-CO-X, Ts-X…). All important aspects of this coupling reaction, including relevant and undesirable side reactions, are evaluated by means of calculations and competitive experiments. The scope and limitations of this method are established.

Synthesis of Fluoroolefins via Julia-Kocienski Olefination

The Julia-Kocienski olefination provides a versatile platform for the synthesis of fluorovinyl compounds. This review describes our efforts as well as those of others in the synthesis of various fluorinated aryl and heteroaryl sulfones and their utility as olefination reagents for the modular assembly of fluoroalkenes. Where data is available, the influence of the fluorine atom on the reactivity of the olefination reagents and the stereochemical outcome of the olefination are described.

Catalytic synthesis of (E)-alpha,beta-unsaturated esters from aldehydes and 1,1-diethoxyethylene

A practical and high yielding synthesis of α,β-unsaturated esters from aldehydes and 1,1-diethoxyethylene was developed.

Fluoro-Julia olefination as a mild, high-yielding route to alpha-fluoro acrylonitriles

Synthesis of a novel, stable reagent (1,3-benzothiazol-2-ylsulfonyl)fluoroacetonitrile from readily synthesized ethyl alpha-(1,3-benzothiazol-2-ylsulfanyl)-alpha-fluoroacetate is reported. Aldehydes undergo condensations with (1,3-benzothiazol-2-ylsulfonyl)fluoroacetonitrile in the presence of DBU leading to alpha-fluoro acrylonitriles in high yields and with good Z-stereoselectivity. Lowering of reaction temperature increases the Z selectivity.

Julia Olefination as a General Route to Phenyl (alpha-Fluoro)vinyl Sulfones

Mild and efficient synthesis of phenyl (alpha-fluoro)vinyl sulfones via condensation of aldehydes and a ketone with a novel benzothiazolyl based bis-sulfone reagent is reported and this proceeds with moderate to good Z-stereoselectivity.

Modified Julia fluoroolefination: selective preparation of fluoroalkenoates

The modified Julia olefination reaction has been applied to develop a stereoselective synthesis of fluoroalkenoate derivatives from a fluorobenzothiazolyl sulfone and aldehydes or a ketone. The olefination reaction can be achieved by using a variety of bases. DBU and DBU in the presence of MgBr2 were found to be the most efficient systems to prepare either (Z)- or (E)-alkenoates in moderate to excellent stereoselectivity.

Exceptionally Mild, High-Yield Synthesis of α-Fluoro Acrylates

Novel achiral and chiral alkyl alpha-(1,3-benzothiazol-2-ylsulfonyl)-alpha-fluoroacetates can be readily synthesized by metalation-fluorination of (1,3-benzothiazol-2-ylsulfonyl)acetates. DBU-mediated condensations of these fluorinated synthons with aldehydes proceed in a facile manner at 0 degrees C or at room temperature giving high yields of alpha-fluoro acrylates. Ketones are unreactive under these conditions. The presence of fluorine renders the synthon substantially more reactive compared to the unfluorinated analogue. Reactivity of alpha-(1,3-benzothiazol-2-ylsulfonyl)-alpha-fluoroacetate and the Horner-Wadsworth-Emmons reagent (EtO)2P(O)CHFCOOEt has also been compared.