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Fluorination reactions are essential to modern medicinal chemistry, thus providing a means to block site-selective metabolic degradation of drugs and access radiotracers for positron emission tomography imaging. Despite current sophistication in fluorination reagents and processes, the fluorination of unactivated CH bonds remains a significant challenge.… (More)
Lanthanide ions, Ln(III), are of interest in the treatment of bone density disorders because they are found to accumulate preferentially in bone (in vivo), have a stimulatory effect on bone formation, and exhibit an inhibitory effect on bone degradation (in vitro), altering the homeostasis of the bone cycle. In an effort to develop an orally active… (More)
A short, 8-step synthesis of the marine natural product pachastrissamine has been developed that relies on a diastereoselective aldol reaction between a suitably protected hydantoin and an optically enriched α-chloroaldehyde. This synthetic route provides new opportunities for exploring structure activity relationships within this family of natural products.
In this paper we address the existence of smooth manifolds proper homotopy equivalent to nonuniform arithmetic manifolds M = Γ\G/K that are not homeomorphic to it. While the manifolds M are properly rigid if rank Q (Γ) ≤ 2, we show that the so-called " virtual structure group " has infinite rank as a Q-vector space if rank Q (Γ) ≥ 4.
Mathai [M] has conjectured that the Cheeger-Gromov invariant ρ (2) = η (2) − η is a homotopy invariant of closed manifolds with torsion-free fundamental group. In this paper we prove this statement for closed manifolds M when the rational Borel conjecture is known for Γ = π 1 (M), i.e. the assembly map α : H * (BΓ, Q) → L * (Γ) ⊗ Q is an isomorphism. Our… (More)
The total synthesis of four candidate stereostructures for the marine octaketide ascospiroketal A have been achieved. These concise and highly stereocontrolled syntheses feature a unique Ag(I) -promoted cyclization cascade involving an oxetanyl ketochlorohydrin to access the entire tricyclic core of the natural product in one step. These syntheses also… (More)
The total synthesis of the marine fungus-derived natural product ascospiroketal is described. This concise synthesis relies on a unique Ag(I) -promoted tandem cascade cyclization that provides direct access to the correctly configured tricyclic core of the natural product from a linear precursor. The synthesis of candidate stereostructures of ascospiroketal… (More)
A silver(I)-promoted intramolecular hemiacetal alkylation has been developed that converts readily available keto-chlorodiols into functionalized spiroacetals containing 5,5-, 5,6-, and 5,7-membered ring systems. The efficiency of this process is demonstrated in a concise total synthesis of the fungal metabolites cephalosporolides E and F.
A concise, stereoselective synthesis of functionalized tetrahydrofuranols has been developed that involves heating readily available chloropolyols in water. These reactions are operationally straightforward and chemoselective for the formation of tetrahydrofurans, obviating the need for complicated protecting group strategies. The efficiency of this process… (More)