Yoshito Kishi

Further synthetic studies on rifamycin s

Abstract Two new highly stereocontrolled syntheses of the optically active form of the aliphatic segment 2 of rifamycin S are described.

On stereochemistry of osmium tetroxide oxidation of allylic alcohol systems: empirical rule

Abstract An empirical formulation is presented to predict the stereochemistry of major osmylation products of allylic alcohols and their derivatives.

Reductive ring openings of allyl-alcohol epoxides

Abstract Red-Al reduction of allyl-alcohol epoxides was shown to yield 1,3-diols in high regioselectivity, while DIBAL reduction was shown to yield 1,2-diols.

Induction of Morphological and Biochemical Apoptosis following Prolonged Mitotic Blockage by Halichondrin B Macrocyclic Ketone Analog E7389

E7389, a macrocyclic ketone analog of the marine natural product halichondrin B, currently is undergoing clinical trials for cancer. This fully synthetic agent exerts its highly potent in vitro and in vivo anticancer effects via tubulin-based antimitotic mechanisms, which are similar or identical to those of parental halichondrin B. In an attempt to understand the impressive potency of E7389 in animal models of human cancer, its ability to induce apoptosis following prolonged mitotic blockage was evaluated. Treatment of U937 human histiocytic lymphoma cells with E7389 led to time-dependent collection of cells in the G2-M phase of the cell cycle, beginning as early as 2 h and becoming maximal by 12 h. Increased numbers of hypodiploid events were seen beginning at 12 h, suggesting initiation of apoptosis after prolonged E7389-induced mitotic blockage. The identity of hypodiploid events as apoptotic cells under these conditions was confirmed by two additional morphologic criteria: green to orange/yellow shifts on acridine orange/ethidium bromide staining, and cell surface annexin V binding as assessed by flow cytometry. Several biochemical correlates of apoptosis also were seen following E7389 treatment, including phosphorylation of the antiapoptotic protein Bcl-2, cytochrome c release from mitochondria, proteolytic activation of caspase-3 and -9, and cleavage of the caspase-3 substrate poly(ADP-ribose) polymerase (PARP). In LNCaP human prostate cancer cells, treatment with E7389 also led to generation of hypodiploid cells, activation of caspase-3 and -9, and appearance of cleaved PARP, indicating that E7389 can activate cellular apoptosis pathways under anchorage-independent and -dependent cell culture conditions. These results show that prolonged mitotic blockage by E7389 can lead to apoptotic cell death of human cancer cells in vitro and can provide a mechanistic basis for the significant in vivo anticancer efficacy of E7389.

Light-emitting properties of recombinant semisynthetic aequorins and recombinant fluorescein-conjugated aequorin for measuring cellular calcium

15 kinds of recombinant semi-synthetic aequorins and a recombinant fluorescein-conjugated aequorin were prepared and their properties in Ca(2+)-triggered luminescence were studied. The semi-synthetic aequorins showed a wide range of Ca(2+)-sensitivity. The luminescence intensity of a high-sensitivity type (hcp-aequorin) was greater than 10(4)-times that of a low-sensitivity type (n-aequorin) at pCa 6.0-6.5. The fluorescein-conjugated aequorin exhibited fluorescence in addition to the Ca(2+)-triggered luminescence, thus it can be used to visualize the diffusion and distribution of aequorin in cells. The data obtained, particularly the Ca(2+)-sensitivity curves, are useful in selecting a suitable semi-synthetic aequorin for an experiment.

Total Synthesis of Altohyrtin A (Spongistatin 1): Part 1

The most active compound of the extraordinarily cytotoxic spongipyrans, spongistatin 1, isolated from marine sponges, appeared to be identical to altohyrtin A. The total synthesis of this macrolide has now firmly established the relative and absolute stereochemistry proposed by Kitagawa (see picture below), and has also verified that altohyrtin A and spongistatin 1 are identical.

On stereochemistry of osmium tetroxide oxidation of allylic alcohol systems: examples

Abstract Forty-two examples are presented to demonstrate the consistency of the empirical formulation proposed in the preceding paper.

A mild preparation of vinyliodides from vinylsilanes

Abstract A new method for the synthesis of vinyliodides from vinylsilanes is presented. Using N-iodiosuccinimide in acetonitrile or acetonitrile/monochloroacetonitrile, this transformation is cleanly effected at room temperature under virtually neutral conditions.

Eribulin Induces Irreversible Mitotic Blockade: Implications of Cell-Based Pharmacodynamics for In vivo Efficacy under Intermittent Dosing Conditions

Eribulin (E7389), a mechanistically unique microtubule inhibitor in phase III clinical trials for cancer, exhibits superior efficacy in vivo relative to the more potent compound ER-076349, a fact not explained by different pharmacokinetic properties. A cell-based pharmacodynamic explanation was suggested by observations that mitotic blockade induced by eribulin, but not ER-076349, is irreversible as measured by a flow cytometric mitotic block reversibility assay employing full dose/response treatment. Cell viability 5 days after drug washout established relationships between mitotic block reversibility and long-term cell survival. Similar results occurred in U937, Jurkat, HL-60, and HeLa cells, ruling out cell type-specific effects. Studies with other tubulin agents suggest that mitotic block reversibility is a quantifiable, compound-specific characteristic of antimitotic agents in general. Bcl-2 phosphorylation patterns parallel eribulin and ER-076349 mitotic block reversibility patterns, suggesting persistent Bcl-2 phosphorylation contributes to long-term cell-viability loss after eribulins irreversible blockade. Drug uptake and washout/retention studies show that [3H]eribulin accumulates to lower intracellular levels than [3H]ER-076349, yet is retained longer and at higher levels. Similar findings occurred with irreversible vincristine and reversible vinblastine, pointing to persistent cellular retention as a component of irreversibility. Our results suggest that eribulins in vivo superiority derives from its ability to induce irreversible mitotic blockade, which appears related to persistent drug retention and sustained Bcl-2 phosphorylation. More broadly, our results suggest that compound-specific reversibility characteristics of antimitotic agents contribute to interactions between cell-based pharmacodynamics and in vivo pharmacokinetics that define antitumor efficacy under intermittent dosing conditions.

Toward Creation of a Universal NMR Database for Stereochemical Assignment: The Case of 1,3,5-Trisubstituted Acyclic Systems

Using the diastereoisomeric triols 1a – d (Fig. 1) and examples summarized in Fig. 2, the central C-atom of acyclic 1,3,5-triols is demonstrated to exhibit a distinctive chemical shift that is dependent on the 1,3- and 3,5-relative configuration, but is independent of the functionalities present outside of this structural motif. These NMR characteristics are then used to predict the relative configuration of several natural products (Fig. 7). In addition, an example is given to show the possibility of assembling an NMR database for a larger array of functional groups from NMR databases of smaller arrays of functional groups.