Gregory R. Dake

Synthetic Studies toward Halichlorine: Complex Azaspirocycle Formation with Use of an NBS-Promoted Semipinacol Reaction

The investigations of a synthetic route incorporating a NBS-promoted semipinacol rearrangement to the 6-azaspiro[4.5]decane fragment within halichlorine ( 1) are presented. A convergent approach was pursued, utilizing two chiral, enantiomerically enriched building blocks, 2-trimethylstannyl piperidene 10 and substituted cyclobutanone 19. Noteworthy synthetic operations in this study include the following: (a) a highly diastereoselective NBS-promoted semipinacol reaction that established four stereogenic centers in ketone 25 and (b) the use of a N- p-toluenesulfonyl-2-iodo-2-piperidene as a precursor to a basic organometallic reagent, which was critical to the success of the coupling of fragments 10 and 19.

Polyamine Transport by the Polyspecific Organic Cation Transporters OCT1, OCT2 and OCT3

Polyamines are ubiquitous organic cations implicated in many physiological processes. Because they are positively charged at physiological pH, carrier-mediated systems are necessary for effective membrane permeation, but the identity of specific polyamine transporter proteins in eukaryotic cells remains unclear. Polyspecific organic cation transporters (OCTs) interact with many natural and xenobiotic monovalent cations and have been reported to transport dicationic compounds, including the short polyamine putrescine. In this study, we used Xenopus oocytes expressing mammalian OCT1 (SLC22A1), OCT2 (SLC22A2), or OCT3 (SLC22A3) to assess binding and transport of longer-chain polyvalent polyamines. In OCT-expressing oocytes, [(3)H]MPP(+) uptake rates were 15- to 35-fold higher than in noninjected oocytes, whereas those for [(3)H]spermidine increased more modestly above the background, up to 3-fold. This reflected up to 20-fold lower affinity for spermidine than for MPP(+); thus, K(0.5) for MPP(+) was ~50 μM in OCT1, ~170 μM in OCT2, and ~60 μM in OCT3, whereas for spermidine, K(0.5) was ~1 mM in OCT1, OCT2, and OCT3. J(max) values for MPP(+) and spermidine were within the same range, suggesting that both compounds are transported at a similar turnover rate. To gain further insight into OCT substrate specificity, we screened a selection of structural polyamine analogues for effect on [(3)H]MPP(+) uptake. In general, blocking potency increased with overall hydrophobic character, which indicates that, as for monovalent cations, hydrophobicity is a major requirement for recognition in polyvalent OCT substrates and inhibitors. Our results demonstrate that the natural polyamines are low affinity, but relatively high turnover, substrates for OCTs. The identification of OCTs as polyamine transport systems may contribute to further understanding of the mechanisms involved in polyamine homeostasis and aid in the design of polyamine-like OCT-targeted drugs.

Chiral Phosphaalkene−Oxazoline Ligands for the Palladium-Catalyzed Asymmetric Allylic Alkylation

Enantioselective catalysis in moderate to excellent yields and ees has been accomplished using a phosphaalkene-based ligand system. Specifically, the palladium-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl acetate using a chiral P(sp(2)),N(sp(2)) ligand proceeds with a variety of malonate nucleophiles in 73-95% yield (79-92% ee).

Gold(I)-catalyzed intramolecular tandem addition/Friedel-Crafts reactions between acyclic enamides and 1-arylalkynes.

Electron-deficient acyclic enamine derivatives react with electron-rich 1-arylalkynes using cationic gold(I) species as catalysts in an intramolecular process to form annulated 1-amido-substituted indene derivatives as the major products. Yields for this process range between 21% and 98%. In some cases, a two-step process that includes a subsequent alkene isomerization is needed.

A Synthetic Approach to the Fusicoccane A-B Ring Fragment Based on a Pauson-Khand Cycloaddition/Norrish Type 1 Fragmentation

A synthetic approach to the A-B ring system within the fusicoccane family of diterpenes is presented. Key steps in this approach are a diastereoselective Pauson-Khand reaction, a Norrish 1 photofragmentation, a Charette cyclopropanation, and a ring-closing metathesis process.

Enamides and Enesulfonamides as Nucleophiles: Formation of Complex Ring Systems through a Platinum(II)-Catalyzed Addition/ Friedel—Crafts Pathway

Cyclic enamine derivatives (enesulfonamides and enamides) tethered to an 1-arylalkynyl fragment undergo a platinum(II)-catalyzed tandem alkyne addition/Friedel-Crafts ring closure to form nitrogen-containing polycyclic structures. Regioselectivity in the initial addition of the enesulfonamide or enamide nucleophile to the platinum(II)-alkyne complex is important. Electron-rich arenes and heterocycles led to the formation of products resulting from an initial 6-endo cyclization. Twenty-three examples of this process are presented.

Enantiomerically Pure Phosphaalkene–Oxazolines (PhAk‐Ox): Synthesis, Scope and Copolymerization with Styrene

The design of a synthetic route to a class of enantiomerically pure phosphaalkene-oxazolines (PhAk-Ox) is presented. The condensation of a lithium silylphosphide and a ketone (the phospha-Peterson reaction) was used as the P=C bond-forming step. Attempted condensation of PhC(=O)Ox (Ox = CNOCH(iPr)CH(2)) and MesP(SiMe(3))Li gave the unusual heterocycle (MesP)(2)C(Ph)=CN-(S)-CH(iPr)CH(2)O (3). However, PhAk-Ox (S,E)-MesP=C(Ph)CMe(2)Ox (1 a) was successfully prepared by treating MesP(SiMe(3))Li with PhC(=O)CMe(2)Ox (52 %). To demonstrate the modularity and tunability of the phospha-Peterson synthesis several other phosphaalkene-oxazolines were prepared in an analogous manner to 1 a: TripP=C(Ph)CMe(2)Ox (1 b; Trip = 2,4,6-triisopropylphenyl), 2-iPrC(6)H(4)P=C(Ph)CMe(2)Ox (1 c), 2-tBuC(6)H(4)P=C(Ph)CMe(2)Ox (1 d), MesP=C(4-MeOC(6)H(4))CMe(2)Ox (1 e), MesP=C(Ph)C(CH(2))(4)Ox (1 f), and MesP=C(3,5-(CF(3))(2)C(6)H(3))C(CH(2))(4)Ox (1 g). To evaluate the PhAk-Ox compounds as prospective precursors to chiral phosphine polymers, monomer 1 a and styrene were subjected to radical-initiated copolymerization conditions to afford [{MesPC(Ph)(CMe(2)Ox)}(x){CH(2)CHPh}(y)](n) (9 a: x = 0.13n, y = 0.87n; GPC: M(w) = 7400 g  mol(-1) , PDI = 1.15).

Total synthesis of cladoniamide G.

The total synthesis of cladoniamide G, a cytotoxic compound against MCF-7 breast cancer cells (10 μg/mL), was accomplished. Key steps in the sequence include oxidative dimerization of 3-acetoxy-5-chloroindole and a tandem process incorporating three steps: bimolecular carbonyl addition, lactam formation, and carbamate removal.

DMAP promoted tandem addition reactions forming substituted tetrahydroxanthones.

Substituted tetrahydroxanthones are constructed using a DMAP-promoted tandem nucleophilic addition process. The reaction yields range from 39% to 73%. Disubstituted tetrahydroxanthones are generated as a ∼2.3:1 mixture of diastereomers favoring the formation of the trans-isomer.

Copper(I) Complexes of Pyridine-Bridged Phosphaalkene-Oxazoline Pincer Ligands

The synthesis of enantiomerically pure pyridine-bridged phosphaalkene-oxazolines ArP═C(Ph)(2,6-C5H3NOx) (1, Ar = Mes/Mes*, Ox = CNOCH(i-Pr)CH2/CNOCH(CH2Ph)CH2) is reported. This new ligand forms a κ(P), κ(2)(NN) dimeric complex with copper(I) (7) that dissociates into a cationic κ(3)(PNN) monomeric complex upon addition of a neutral ligand {[1a·CuL]OTf (8a-e): L = PPh3 (a), P(OPh)3 (b), 2,6-lutidine (c), 4-DMAP (d), 1-methylimidazole (e)}. The P-Cu bond lengths in 8 are influenced by the π-accepting/σ-donating properties of L, and this can be observed by changes in the δ(31)PP═C NMR shift. The donor-acceptor properties in complexes of type 8 have also been investigated by UV/vis spectroscopy and density functional theory calculations.