Asymmetric synthesis of a potent azepanone-based inhibitor of the cysteine protease cathepsin K

In this account we detail the asymmetric synthesis of 1, a potent azepanone-based inhibitor of cathepsin K (K_i = 0.16 nM), which has been shown to inhibit the production of biomarkers of bone resorption in monkeys. The key steps in the synthesis sequence were the utility of the Evans aldol reaction coupled with the ring closing olefin metatheses to assemble the azepanone core contained within 1.     

Practical asymmetric synthesis of a potent Cathepsin K inhibitor. Efficient palladium removal following Suzuki coupling

A large-scale, chromatography-free synthesis of a potent and selective Cathepsin K inhibitor 1 is reported. The key asymmetric center was installed by addition of (R)-pantolactone to the in situ-generated ketene 4a. The final step of the convergent synthesis of 1 was completed via Suzuki coupling of aryl bromide 7a with unprotected aryl piperazine boronic acid 13. Residual palladium and iron generated in the Suzuki coupling were efficiently removed from crude 1 via a simple extractive workup using lactic acid.     

Efficient enantioselective synthesis of sertraline, a potent antidepressant, via a novel intramolecular nucleophilic addition to imine

[formula: see text] An efficient enantioselective synthesis of sertraline, an antidepressant, utilizing anionic imine ring closure is described.     

Practical synthesis of a potent hepatitis C virus RNA replication inhibitor

A practical, efficient synthesis of 1, a hepatitis C virus RNA replication inhibitor, is described. Starting with the inexpensive diacetone glucose, the 12-step synthesis features a novel stereoselective rearrangement to prepare the key crystalline furanose diol intermediate. This is followed by a highly selective glycosidation to couple the C-2 branched furanose epoxide with deazapurine.     

Large-scale synthesis of SB-462795, a cathepsin K inhibitor: the RCM-based approaches

Two stereoselective syntheses of SB-462795, a highly potent cathepsin K inhibitor, are described. Both routes feature a C5-C6 disconnection by ring closing metathesis to construct an azepane ring and are amenable to large-scale manufacturing.     

Synthesis of 3-oxooxa- and 3-oxoazacycloalk-4-enes by ring-closing metathesis. Application to the synthesis of an inhibitor of cathepsin K

3-Oxooxa- and 3-oxoazacycloalk-4-enes were obtained with good yield from 1-(ω-alkenyloxy)- and 1-(ω-alkenylamino)-but-3-en-2-ones by using a ring-closing metathesis. This methodology has been used to synthesize an inhibitor of cathepsin K.     

Practical application of new catalytic methods: a concise synthesis of a potent PDE IV inhibitor

An efficient synthesis of a potent PDE IV inhibitor 1 is described. The synthesis is highlighted by two practical and efficient catalytic reactions: a highly selective catalytic palladium mediated carbonylation of the pyridine side chain and an efficient palladium-catalyzed Suzuki-Miyaura coupling of a chloropyridine-N-oxide.     

Practical synthesis of a peptidomimetic thrombin inhibitor

Compound 1 is a low molecular weight thrombin inhibitor developed for treatment of deep vein thrombosis and cardiovascular diseases. We herein report our efforts to develop a robust, efficient and reproducible process suitable for large-scale synthesis of compound 1.     

Practical synthesis of an orally active renin inhibitor aliskiren

A convergent synthesis of aliskiren was accomplished via the use of Segment AB as the key intermediate, which was prepared via the coupling of the Grignard reagent derived from Segment B with Segment A, followed by subsequent oxidative lactonization.     

Diastereoselective addition of alkynylalanes to carbohydrate-derived nitrones

Propargylic N-hydroxypyrrolidines were prepared by diastereoselective addition of pre-formed alkynylalanes to various highly functionalized carbohydrate-derived endocyclic nitrones. Excellent diastereoisomeric excesses were obtained using dimethyl-2-phenylethynylalane. Addition of other alkynylalane derivatives to such type of nitrones is also reported.     

Diastereoselective addition of alcohol to diastereotopic silylenes

The successful example of diastereoselective addition of alcohol to diastereotopic silylenes is reported.     

Diastereoselective addition of HCN to Garner's aldehyde

The hydrocyanation of N-Boc-N,O-isopropylidene-l-serinal 1 (Garner's aldehyde) is described. The influence of various reaction conditions (solvent, temperature, addition of a Lewis acid, presence of a biocatalyst) on the stereochemical outcome of the addition of HCN was investigated. The use of 2-pentanol as the solvent at room temperature afforded complete stereoselectivity. X-Ray analysis of the product showed the anti configuration. The results can be readily explained on the basis of a Felkin–Anh type model.     

Diastereoselective addition of γ-alkylthio-allylboronates to aldehydes

The Z- and E-γ-alkylthio-allylboronates $\text{5}$ and $\text{10}$ were found to add aldehydes forming diastereoselectively the adducts $\text{7}$ and $\text{6}$ respectively in high yield.     

Practical synthesis of a neuropeptide Y antagonist via stereoselective addition to a ketene

[Reaction: see text]. The synthesis of neuropeptide Y antagonist 1, currently under clinical investigation for the treatment of obesity, is described. The convergent synthesis from trans-spirolactone carboxylic acid intermediate 2a and aminopyrazole 3 is predicated on a stereoselective route to the former. The coupling reaction of ethyl 4-oxocyclohexanecarboxylate (10a) with lithiated isonicotinamide 11 was investigated in detail, but even optimized conditions only provided a 45:55 ratio of trans:cis isomers (12a:12b). While selective crystallization schemes were developed to isolate the thermodynamically less stable trans isomer 2a, improved stereocontrol was subsequentially achieved by the application of ketene chemistry. The ketene formation and quench was investigated under a variety of conditions aimed at maximizing the trans:cis ratio. Reacting a mixture of carboxylic acids 2a and 2b with POCl3 in THF, followed by concomitant addition of tert-butyl alcohol in the presence of TMEDA at 35 degrees C provided a 4:1 ratio of trans:cis tert-butyl esters (18a:18b) via in situ ketene formation. Ester hydrolysis, followed by selective crystallization of undesired 2b as the HCl salt, led to isolation of 2a in 47% overall yield. Aminopyrazole intermediate 3 was synthesized via the condensation reaction of 2-fluorophenylhydrazine hydrochloride (4a) with acrylonitrile derivative 5 in 65-70% yield. Coupling of advanced intermediates 2a and 3b via activation with thionyl chloride gave a 92% yield of 1.     

Diastereoselective addition of allyltitanocenes to cyclic enones

The reaction of allyltitanocenes with five- to seven-membered cyclic enones proceeded with good to high diastereoselectivity depending on the ring size of enones. The stereochemistry of the major isomers produced by the reaction of cinnamyltitanocene was opposite to that of crotyltitanocene.     

Practical asymmetric synthesis of a potent PDE4 inhibitor via stereoselective enolate alkylation of a chiral aryl-heteroaryl secondary tosylate

A practical, chromatography-free catalytic asymmetric synthesis of a potent and selective PDE4 inhibitor (L-869,298, 1) is described. Catalytic asymmetric hydrogenation of thiazole ketone 5a afforded the corresponding alcohol 3b in excellent enantioselectivity (up to 99.4% ee). Activation of alcohol 3b via formation of the corresponding p-toluenesulfonate followed by an unprecedented displacement with the lithium enolate of ethyl 3-pyridylacetate N-oxide 4a generated the required chiral trisubstituted methane. The displacement reaction proceeded with inversion of configuration and without loss of optical purity. Conversion of esters 2b to 1 was accomplished via a one-pot deprotection, saponification, and decarboxylation sequence in excellent overall yield.     

Diastereoselective intermolecular addition of the 1,3-dioxolanyl radical to N-acyl aldohydrazones. Asymmetric synthesis of alpha-amino acid derivatives

[reaction: see text] N-Acyl aldohydrazones I (R = CO(2)Et, alkyl, aryl, and furyl) efficiently trap the 1,3-dioxolanyl radical intermolecularly without external activation at temperatures as low as -78 degrees C. For alkyl aldohydrazones, good diastereoselectivities are obtained in the presence of InCl(3) at low temperature. Elaboration of the adducts (II) allows for the asymmetric synthesis of alpha-amino acid derivatives.     

Diastereoselective synthesis of delta-aminoacids through domino Ireland-Claisen rearrangement and Michael addition

A novel domino reaction--stereoselective Ireland-Claisen rearrangement and asymmetric Michael addition--is described. A protocol starting from Baylis-Hillman adducts 3a-f using chiral lithium amide affords optically active gamma-substituted delta-amino acids 4a-f with high diastereoselectivities and enantioselectivities. The acid can be isolated easily from large-scale reactions and transformed to 2,3-disubstituted piperidines 11 or 2-substituted nipecotic acid derivates 12.     

Diastereoselective addition of organomanganese compounds to chiral polyalkoxyaldehydes

Organomanganese compounds RMnI (R=Me, Pr, Bu, Hex, Ph, BuCC) prepared from RLi and MnI₂ in Et₂O react with 3-O-benzyl-1,2-O-isopropylidene--D-xylo-pentodialdo-1, 4-furanose, 1,23,4-di-O-isopropylidene--D-galacto-hexodialdo-1,5-pyranose, andR-2,3-dibenzyloxypropanal to afford 4,5-threo-, 5,6-threo-, and 2,3-threo-isomeric products, respectively, with high diastereoselectivity.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1122–1126, June, 1993.     

Diastereoselective addition of arylzinc reagents to sugar aldehydes

The diastereoselective arylation of sugar-derived aldehydes is described. The arylating reagents are generated in situ by a boron-to-zinc exchange reaction of arylboronic acids with Et(2)Zn to generate arylethylzinc reagents. The exquisite reactivity of the arylzinc reagents allowed for an efficient and mild arylation, delivering the corresponding products in diastereoisomeric ratios of up to >20:1. The utility of the methodology is highlighted with an efficient formal synthesis of (+)-7-epi-goniofufurone, a member of the styryllactone family of natural products.