Horner-Emmons Olefination Research Articles

Asymmetric synthesis of ENT-03, the predicted mammalian ortholog of the dog fish shark aminosterol trodusquemine (MSI-1436)

ENT-03 was predicted to be the mammalian equivalent of trodusquemine, based on knowledge of the bile acids produced in mammals, such as 7-HOCA. The individual C-25 isomers of ENT-03 were prepared and both isomers were detected in neonatal mouse brain and liver. Trodusquemine and ENT-03 have both demonstrated dramatic effects in obesity and insulin resistance. (25S)-ENT-03 was selected for development for the treatment of diabetes and obesity. In this paper the first synthesis of this putative natural product is described. Starting with a stereo-defined steroidal intermediate 2, the semi-synthesis involves three stereoselective steps: Horner-Emmons olefination, hydrogenation, and reductive amination. Asymmetric hydrogenation using a ruthenium coordinated Mandyphos ligand was found to be effective in controlling the C25-stereochemistry of both isomers. The syntheses of the ENT-03 isomers and a deuterated reference standard facilitated identification and quantification of this natural product in mouse tissues, and exploration of its therapeutic potential.

Design, synthesis and anti-melanogenic effect of cinnamamide derivatives.

Pigmentation disorders are attributed to excessive melanin which can be produced by tyrosinase. Therefore, tyrosinase is supposed to be a vital target for the treatment of disorders associated with overpigmentation. Based on our previous findings that an (E)-β-phenyl-α,β-unsaturated carbonyl scaffold can play a key role in the inhibition of tyrosinase activity, and the fact that cinnamic acid is a safe natural substance with a scaffolded structure, it was speculated that appropriate cinnamic acid derivatives may exhibit potent tyrosinase inhibitory activity. Thus, ten cinnamamides were designed, and synthesized by using a Horner-Emmons olefination as the key step. Cinnamamides 4 (93.72% inhibition), 9 (78.97% inhibition), and 10 (59.09% inhibition) with either a 2,4-dihydroxyphenyl, or 4-hydroxy-3-methoxyphenyl substituent showed much higher mushroom tyrosinase inhibition at 25 µM than kojic acid (18.81% inhibition), used as a positive control. Especially, the two cinnamamides 4 and 9 having a 2,4-dihydroxyphenyl group showed the strongest inhibition. Docking simulation with tyrosinase revealed that these three cinnamamides, 4, 9, and 10, bind to the active site of tyrosinase more strongly than kojic acid. Cell-based experiments carried out using B16F10 murine skin melanoma cells demonstrated that all three cinnamamides effectively inhibited cellular tyrosinase activity and melanin production in the cells without cytotoxicity. There was a close correlation between cellular tyrosinase activity and melanin content, indicating that the inhibitory effect of the three cinnamamides on melanin production is mainly attributed to their capability for cellular tyrosinase inhibition. These results imply that cinnamamides having the (E)-β-phenyl-α,β-unsaturated carbonyl scaffolds are promising candidates for skin-lighting agents.

A facile synthesis of (E)-2-(aryl/hetaryl)vinyl-4-phenylquinoline-3-carboxylic acids

Abstract New synthetic approach to (E)-2-aryl/hetarylvinyl-4-phenyl-quinoline-3-carboxylic acids was developed, featuring three different synthetic transformations, namely the Arbuzov reaction, in situ Horner-Emmons olefination and subsequent ester hydrolysis occurring as a one-pot procedure. The molecular structures of newly synthesized products were confirmed by spectral data and elemental analysis.

Total synthesis of 5-epi-Torrubiellutin C and its biological evaluation

The total synthesis of 5-epi-Torrubiellutin C is described in a fully stereocontrolled manner and linear sequence involving high yielding steps. The synthetic strategy involves the dicyclohexylboron chloride mediated Paterson's aldol protocol, Horner–Emmons olefination, TiCl4 mediated syn-aldol reaction and ring closing metathesis (RCM) as the key steps. Furthermore, the resultant epimer was evaluated for cytotoxicity against DU145 (prostate), MCF-7 (breast) and A549 (lung) cancer cell lines, and the results showed that the 5-epi-Torrubiellutin C is as good as the natural product in bioassays.

Tandem application of C-C bond-forming reactions with reductive ozonolysis.

Several variants of reductive ozonolysis, defined here as the in situ generation of aldehydes or ketones during ozonolytic cleavage of alkenes, are demonstrated to work effectively in tandem with a number of C-C bond-forming reactions. For reactions involving basic nucleophiles (1,2-addition of Grignard reagents, Wittig or Horner-Emmons olefinations, and directed aldol reactions of lithium enolates), the one-pot process offers a rapid and high-yielding alternative to traditional two-step protocols.

Synthesis of the spiroketal fragment of bistramide A via an exocyclic enol ether

An efficient synthesis of the spirocyclic fragment 1 of bistramides is reported. An olefination reaction of lactone 4 with sulfone 5 gave the enol ether 3, which upon cyclization in acidic media provided the spiroketal ring system. This compound was then converted into the C19–C36 fragment of the bistramides via successive Julia–Kocienski and Horner–Emmons olefinations.

A facile synthesis of 5,6-dihydro-5-hydroxy-2(1 H)-pyridone

A short synthesis of 5,6-dihydro-5-hydroxy-2(1 H)-pyridone was achieved from l-serine employing Horner–Emmons olefination as the key step.

Synthesis of Z‐N‐Alkenylformamides

Commercially available difluorinated benzaldehyde was converted to the Z‐N‐alkenylformamides via Horner–Emmons olefination and Curtius rearrangement, followed by reduction with tri‐tert‐butoxy‐aluminohydride.

Synthesis of novel keto-ACE analogues as domain-selective angiotensin I-converting enzyme inhibitors

Novel analogues of the angiotensin I-converting enzyme (ACE) inhibitor keto-ACE were synthesized via a facile Horner–Emmons olefination of a phosphonoketone precursor with ethyl glyoxylate. Introduction of a bulky aromatic tryptophan at the P 2 ′ position of keto-ACE resulted in a significant increase in C-domain-selectivity.

Thrombomodulin induction in cultured human endothelial cells by 9- cis-locked retinoic acid analogues

9- cis-Retinoic acid (RA) analogues devised to lock the 9- cis double bond by ring formation were synthesized using two stereoselective carbon–carbon bond formation reactions as key steps. The palladium-mediated Suzuki reaction was adopted to construct a 7 E-double bond (RA numbering) and the Horner–Emmons olefination was employed for stereoselective 11 E-double bond (RA numbering) formation. The synthesized 9- cis-RA analogues that are locked by five-membered ring systems (cyclopentene, dihydrofuran, and dihydrothiophene) were shown to have comparable thrombomodulin induction activities to that of 9- cis RA. Conformational analysis of these compounds showed their similarity to 9- cis RA in the spatial orientation of the side chain and the terminal carboxy group.

Synthesis of constrained analogues of cholecystokinin/opioid chimeric peptides

In our ongoing research on the synthesis of constrained analogues of CCK/opioid chimeric peptides, a bicyclic dipeptide mimetic for Nle-Asp was designed and synthesized. Starting from β-allyl substituted aspartic acids, the terminal double bond was oxidized resulting in spontaneous cyclization to form racemic hemiaminals. Allylation of the hemiaminals afforded 5-allyl substituted proline analogues, which on oxidation, Horner–Emmons olefination, asymmetric hydrogenation, and bicyclization afforded bicyclic dipeptide mimetics for Nle-Asp. Constrained CCK/opioid peptide analogues containing bicyclic dipeptide mimetics for Nle-Gly, Nle-Asp, and homoPhe-Gly were then synthesized and analyzed at both the CCK and opioid receptors.

Stereoselective Total Synthesis of the Natural (+)‐Lasonolide A

AbstractFor Abstract see ChemInform Abstract in Full Text.

Application of Horner–Emmons Olefination to the Crown-Ether Derivatives

An effective synthetic approach to the preparation of a new crown-ether vinylogs involving the Horner–Emmons olefination of carbonyl precursors with the use of C2- and C5-phosphonates was proposed. The effects of the conjugation chain length and the nature of the terminal polar functions in the phosphonate reagent on the yield and process stereoselectivity were discussed.

Stereoselective Total Synthesis of the Natural (+)-Lasonolide A

The natural (+)-lasonolide A (1), an anti-tumor agent, has been synthesized via thermodynamic benzylidene formation at the C 2 2 quaternary chiral center, use of a disulfone equivalent for elongation of the C 1 5 -C 1 7 three-carbon chain as well as introduction of the two trans olefins at C 1 5 and C 1 7 , iodocyclization for the upper THP. Michael addition for the bottom THP, and intramolecular Horner-Emmons olefination for the 20-membered macrolactone.

Design, synthesis and preliminary evaluation of peptidomimetic inhibitors of HIV aspartic protease with an epoxyalcohol core

Two peptidomimetic inhibitors based on a novel epoxyalcohol core were designed to target the epoxide ring at the catalytic aspartates of HIV-protease for irreversible inhibition of the enzyme. The inhibitors were synthesized with a multi-step approach which includes Horner-Emmons olefination of a phenylalanine-derived phosphono ketone, stereoselective reduction of the resulting trans-enones to allylic alcohols and syn-epoxidation of the latters. The epoxyalcohols thus obtained were assayed for their ability to inhibit HIV-PR and were shown to inhibit the protease with IC50 values of 39 and 150 µM, respectively. This confirms that the designed epoxides are recognised with fairly good affinity by the enzyme’s active site, a pre-requisite for selective irreversible inhibition.

Synthesis of Chiral 3,4‐Disubstituted Pyrroles from L‐Amino Acids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Polymer/carrier composites as materials and reactors for organic synthesis

In this work new polymer/carrier composites are described which serve as novel materials in flow-through reactors for polymer-supported organic solution-phase synthesis. Monolithic polymer/carrier columns are prepared by a new precipitation polymerization process inside the void pore volume of megaporous glass carrier materials. Chemical functionalization of the internal polymer phase with chlorosulfonic acid or trimethylamine generates small, interconnected ion-exchange resin beads with a diameter of 1–3 μm which can be used for a large variety of organic syntheses. These monolithic rods are incorporated into an appropriate casing and can conveniently be operated in the flow-through mode. Important successful applications are polymer-assisted solution-phase reductions, oxidations and Horner–Emmons olefinations. Additionally, the use of these monolithic columns as catalytic microreactors and their performance in selected reactions are described.

Enantioselective Total Synthesis of the Antitumor Macrolide Rhizoxin D

The convergent, highly enantioselective synthesis of rhizoxin D, a natural product possessing potent antitumor and antifungal bioactivity, is described. The C(1)-C(9) fragment of the molecule was synthesized utilizing a threefold pseudosymmetric intermediate ultimately derived from gamma-butyrolactone. The central core of rhizoxin D was prepared via a chiral resolution/asymmetric aldol protocol. Several methods for the generation of the polyene fragment were explored, and the side-chain was ultimately prepared from serine in six steps. The unification of the left and right wings of the molecule was achieved using a one-step olefination protocol, and the macrocyclization was carried out using a Horner-Emmons olefination at the C(2)-C(3) olefin.

Total synthesis of (+)-asteltoxin.

A convergent synthesis of (+)-asteltoxin (1) has been achieved by the Horner-Emmons olefination of bis(tetrahydrofuran) aldehyde 53 and alpha-pyrone phosphonate 5. A key step features the stereoselective construction of a sterically congested quaternary center embedded in the densely functionalized bis(tetrahydrofuran) subunit by a Lewis acid-catalyzed, pinacol-type rearrangement of an epoxy silyl ether. This pivotal rearrangement methodology parallels the proposed biosynthetic pathway of 1 and is ripe for applications to the stereocontrolled synthesis of structurally complex natural products.

Synthesis of Chiral 3,4-Disubstituted Pyrroles from L-Amino Acids

A general methodology for the conversion of naturally occurring amino acids to 3,4-disubstituted pyrroles is described. A suitably protected amino acid (1) was first converted to the corresponding aldehyde (2). HornerEmmons olefination afforded a facile entry to the corresponding α,β-unsaturated ester (3). The construction of the pyrrole ring system was accomplished in a single step, using an intramolecular cyclization reaction with tosylmethyl isocyanide (TOSMIC).