Synthesis of 7-Substituted Benzolactam-V8s and Their Selectivity for Protein Kinase C Isozymes

Condensation of l-valine benzyl ester toluenesulfonic acid salt with a substituted cyclohexadione followed by aromatization with the assistance of NBS provides an N-aryl l-valine benzyl ester. This intermediate is converted into 7-substituted benzolactam-V8s using an asymmetric Strecker reaction as the key step. The target molecules show a different pattern of isozyme selectivity relative to the 8-substituted benzolactam-V8s

Studies in Polyphenol Chemistry and Bioactivity. 2. Establishment of Interflavan Linkage Regio- and Stereochemistry by Oxidative Degradation of an <i>O</i>-Alkylated Derivative of Procyanidin B₂ to (<i>R</i>)-(−)-2,4-Diphenylbutyric Acid

The assignment of interflavan bond regio- and stereochemistry in oligomeric proanthocyanidins has in the past relied on empirical spectroscopic techniques which are influenced by the conformation of the C rings. Only recently was the 4,8-regiochemistry of procyanidin B2 (3b) firmly established by 2-dimensional NMR methods. We describe herein the proof of 4β-stereochemistry in 3b by oxidative degradation of the derivative 3d bearing differential (O-benzyl and O-methyl) protecting groups in its “top” and “bottom” epicatechin moieties, to (R)-(−)-2,4-diphenylbutyric acid. The key elements of the degradative process are (1) removal of the C-3 alcohol functions through a modified Barton deoxygenation employing hypophosphorous acid as the reducing agent; (2) deprotection of the “top” unit by hydrogenolysis, followed by exhaustive aryl triflate formation with N,N-bis(trifluoromethanesulfonyl)aniline and DBU in DMF; (3) hydrogenolytic deoxygenation of the “top” unit over Pearlman's catalyst with concomitant scission of the O−C2 bond; (4) selective oxidation of the “bottom” unit with NaIO4/RuCl3. The hitherto unreported absolute configuration of (−)-2,4-diphenylbutyric acid was established as R by X-ray crystal structure analysis of the (R)-(+)-α-methylbenzylamine salt. As a corollary, the selectivity of hydrogenolytic and solvolytic reactions of epicatechin-derived tetrasulfonates has been investigated

Studies in Polyphenol Chemistry and Bioactivity. 1. Preparation of Building Blocks from (+)-Catechin. Procyanidin Formation. Synthesis of the Cancer Cell Growth Inhibitor, 3-<i>O</i>-Galloyl-(2<i>R</i>,3<i>R</i>)-epicatechin-4β,8-[3-<i>O</i>-galloyl-(2<i>R</i>,3<i>R</i>)-epicatechin]

A project has been initiated to synthesize proanthocyanidin oligomers found in cocoa. Natural, readily available (+)-catechin was transformed into 5,7,3‘,4‘-tetra-O-benzyl-(−)-epicatechin (14) by (a) benzylation of the phenolic oxygens; (b) oxidation of the 3-alcohol to ketone by the Dess−Martin periodinane; and (c) reduction with lithium tri-sec-butylborohydride (l-Selectride) in the presence of LiBr. The additive diminishes the extent of ketone enolization while maintaining a stereoselectivity of ≥200:1. Oxidation of 14 with DDQ was performed best from the standpoint of product purification if ethylene glycol was used as the nucleophilic trapping agent. The resulting ether 19 was condensed with 14 using TiCl4 to give a good yield of benzyl-protected epicatechin-4β,8-epicatechin (octa-O-benzylprocyanidin B2, 20) as the sole dimeric product. Hydrogenolysis of 20 yielded procyanidin B2 in the first enantiospecific synthesis of this natural product which employs protected intermediates and thereby allows the necessary product separation after the condensation step to be performed on nonpolar, nonsensitive intermediates. Acylation of 20 with tri-O-benzylgalloyl chloride followed by hydrogenolysis gave access to the title bis-gallate (24). This constitutes the first synthesis of this natural product, a compound notable for its PKC-inhibitory and anticancer activity

A Tandem Michael Addition Ring-Closure Route to the Metabotropic Receptor Ligand α-(Hydroxymethyl)glutamic Acid and Its γ-Alkylated Derivatives

A Tandem Michael Addition Ring-Closure Route to the Metabotropic Receptor Ligand α-(Hydroxymethyl)glutamic Acid and Its γ-Alkylated Derivative

A Tandem Michael Addition Ring-Closure Route to the Metabotropic Receptor Ligand α-(Hydroxymethyl)glutamic Acid and Its γ-Alkylated Derivatives

A Tandem Michael Addition Ring-Closure Route to the Metabotropic Receptor Ligand α-(Hydroxymethyl)glutamic Acid and Its γ-Alkylated Derivative

Dipolar Cycloaddition Route to Diverse Analogues of Cocaine: The 6- and 7-Substituted 3-Phenyltropanes

In our quest for an antagonist or partial agonist of cocaine, access to certain 6- and 7-substituted 3-phenyltropanes of type I was required. Starting from 3-hydroxy-1-methyl-4-phenylpyridinium iodide, we disclose a pyridinium betaine-based dipolar cycloaddition route to tropenones of type II. In turn, we show how this intermediate can be transformed to type I products either through the copper-catalyzed conjugate addition reaction of Grignard reagents to the enones 7−9 or by the copper(I)-catalyzed cross coupling reaction of the allylic acetates 15a and 16a with Grignard reagents

Design and Synthesis of a Potent and Selective Peptidomimetic Inhibitor of Caspase-3

In this paper we report the synthesis and characterization of a novel potent and selective inhibitor of caspase-3, a member of the caspase family of cysteine proteases which plays an important role in many human disorders. This molecule represents 3(S)-acetylamino-N-{1-[(((3S)-2-hydroxy-5-oxo-tetrahydrofuran-3-yl)carbamoyl)methyl]-2-oxo-5-phenyl-2,3-dihydro-1H-benzo[e][1,4]diazepin-3-yl}succinamic acid, a monocyclic conformationally constrained form of the tetrapeptide Ac-DEVD-H, in which a 1,4-benzodiazepine nucleus is introduced internally to the peptidic sequence

Studies in Polyphenol Chemistry and Bioactivity. 4. Synthesis of Trimeric, Tetrameric, Pentameric, and Higher Oligomeric Epicatechin-Derived Procyanidins Having All-4β,8-Interflavan Connectivity and Their Inhibition of Cancer Cell Growth through Cell Cycle Arrest¹

We report an improved synthesis of bis(5,7,3‘,4‘-tetra-O-benzyl)epicatechin 4β,8-dimer (3) from 5,7,3‘,4‘-tetra-O-benzylepicatechin (1) and 5,7,3‘,4‘-tetra-O-benzyl-4-(2-hydroxyethoxy)epicatechin (2) by replacing the previously employed Lewis acid, titanium tetrachloride, with the clay mineral Bentonite K-10. Under the same conditions, the benzyl-protected all-4β,8-trimer, -tetramer, and -pentamer were obtained regioselectively from their lower homologues, albeit in rapidly decreasing yields. Reaction of 2 with an organoaluminum thiolate generated from 2-mercaptobenzothiazole and trimethylaluminum followed by acetylation produced 3-O-acetyl-4-[(2-benzothiazolyl)thio]-5,7,3‘,4‘-tetra-O-benzylepicatechin (12). Medium-sized protected oligomers with 4β,8-interflavan linkages are obtained in improved yields by using this compound as the electrophile and silver tetrafluoroborate as activator and are isolated by reversed-phase HPLC. Their deprotection by ester saponification followed by hydrogenolysis yielded the free procyanidins, which were characterized as their peracetates. The synthetic procyanidins are identical by normal-phase HPLC with fractions isolated from cocoa. The principle of chain extension by two members was demonstrated using a dimeric electrophile obtained by self-condensation of compound 12. Both the synthetic and natural pentamer 32 inhibit the growth of several breast cancer cell lines. Using the MDA MB 231 line, it was established that this outcome is based on the induction of cell cycle arrest in the G0/G1 phase. Subsequent cell death is more likely necrotic rather than apoptotic. Control experiments demonstrate that the polyphenol itself, rather than hydrogen peroxide potentially formed by its autoxidation, is the causative agent

Applications of Organosulfur Chemistry to Organic Synthesis: Total Synthesis of (+)-Himbeline and (+)-Himbacine

Total syntheses of (+)-himbacine (1) and (+)-himbeline (2) are described. The synthesis involves the preparation of sulfone 38 and aldehyde 42 as single enantiomers followed by coupling of these compounds using a Julia−Lythgoe olefination. The preparation of sulfone 38 features an acid-promoted intramolecular Diels−Alder reaction of an α,β-unsaturated thioester while the synthesis of 42 features a Beak alkylation of piperidine 39

Applications of Organosulfur Chemistry to Organic Synthesis: Total Synthesis of (+)-Himbeline and (+)-Himbacine

Total syntheses of (+)-himbacine (1) and (+)-himbeline (2) are described. The synthesis involves the preparation of sulfone 38 and aldehyde 42 as single enantiomers followed by coupling of these compounds using a Julia−Lythgoe olefination. The preparation of sulfone 38 features an acid-promoted intramolecular Diels−Alder reaction of an α,β-unsaturated thioester while the synthesis of 42 features a Beak alkylation of piperidine 39