The integration of a chromogenic reporter group into the recently reported (Zimmerman, S. C.; Wendland, M. S.; Rakow, N. A.; Zharov, I.; Suslick, K. S. Nature 2002, 418, 399-403) monomolecular imprinting approach is described. The resulting highly cross-linked, macromolecular hosts show rapid, selective, high affinity, two-point binding of straight-chain diamine guests. Over longer times, the hosts are more promiscuous, binding a broader range of diamines. A rigorous test of imprinting was performed wherein the cross-reactivities of two dendrimers derived from different templates are compared. The test reveals a guest-dependent kinetic binding effect masquerading as evidence of a highly selective two-point imprinting process.

[reaction: see text] The protiodesilylation of unactivated C(sp3)-SiMe2Ph bonds proceeds efficiently by treatment with tetrabutylammonium fluoride in wet DMF or THF via isolable dimethylsilanol intermediates.

[reaction: see text] (Trifluoroacetyl)azobenzene dyes were previously employed as amine reporter groups (chemosensors) in a dendrimer-based monomolecular imprinting system. Kinetic and binding studies with a range of amines and diamines show that the highly selective signaling observed for alkane diamines by these imprinted dendrimers arises from a kinetic effect due to intramolecular general base-catalyzed carbinolamine formation with the dye itself. The relationship between diamine structure and carbinolamine stability and rate of formation is described.

A total synthesis of (+)-bullatacin has been accomplished via a diastereoselective [3+2] annulation reaction of the highly enantiomerically enriched allylsilane 3 and racemic aldehyde 4, which provides the key bis-tetrahydrofuran fragment 15 with ≥ 20 : 1 ds.(+)-Bullatacin (1) is one of more than 350 Annonaceous acetogenins isolated from the tropical plant family Annonaceae (Figure 1). Many members of this structurally diverse family of natural products exhibit impressive antitumor activity in human tumor cell lines. 1 The acetogenins contain a long aliphatic backbone bearing a terminal butenolide unit and one or more tetrahydrofuran rings and hydroxyl groups at internal positions of the aliphatic chain. These compounds are intriguing synthetic targets owing to the variation of stereochemistry around the tetrahydrofuran rings and at the sites bearing additional hydroxyl groups. 2, 3The [3+2]-annulation reaction of aldehydes and chiral allylsilanes is an important method for the stereocontrolled synthesis of substituted tetrahydrofurans. 4, 5 β-Silyloxy-substituted allylsilanes undergo [3+2] annulation reactions with aldehydes and certain electrophilic ketones to give either 2, 5-trans or 2, 5-cis substituted tetrahydrofurans with excellent selectivity, depending on the use of chelating or non-chelating Lewis acids, respectively. 6 We have recently utilized this methodology in a highly stereoselective total synthesis of asimicin (2). 7As part of ongoing studies focusing on the development of a stereochemically general synthesis of members of the acetogenin family, we have developed and report herein a highly stereoselective synthesis of bullatacin (1), 8 which differs from asimicin (2) at a single stereocenter (C-24). We envisaged that the bis-tetrahydrofuran core unit of bullatacin could be synthesized from sequential chelate-controlled [3+2] annulation reactions of allylsilanes 3 and 6 (Figure 2). The proposed [3+2] annulation of 3 and 4 is expected to be a stereochemically matched double asymmetric reaction under chelate-controlled conditions, by analogy with the corresponding reaction in our asimicin synthesis that proceeded with ≥20 : 1 ds. 7The erythro stereochemistry of C(23)-C(24) of aldehyde 4 requires that a syn-β-silyloxy allylsilane 6 be used in a chelate-controlled [3+2] annulation reaction with α-benzyloxy acetaldehyde (5). Initial attempts to develop an enantioselective synthesis of syn-β-silyloxy allylsilanes related to 6 focused on asymmetric allylboration reactions using (Z)-γ-dimethylphenylsilyallylboronate 7 (Scheme 1). Thus, silylcupration 9 of acetylene, addition of ‡ Address correspondence to this author at Scripps Florida, Department of Medicinal Chemistry, 5353 Parkside Drive, RF-2, Jupiter, FL 33485; e-mail: roush@scripps.edu. A more convenient route to (racemic) syn-β-hydroxyallylsilanes 8 involves the γ-silylallylstannation of aldehydes using γ-(dimethylphenylsilyl)allylstannane 9. 12 Treatment of cyclohexanecarboxaldehyde with 9 at −78 °C in CH 2 Cl 2 in the presence of BF 3 ·...

Hydrogen-bond-mediated complexation of a CG base pair by a hexylureido phthalimide and a hexylureido isoindolin-1-one was studied by (1)H NMR spectroscopy in an organic solvent. Chemical shift data indicate that both receptors effectively bind the CG base pair from the major groove side.