Synthesis of 6-Halo-Substituted Pericosine A and an Evaluation of Their Antitumor and Antiglycosidase Activities

The enantiomers of 6-fluoro-, 6-bromo-, and 6-iodopericosine A were synthesized. An efficient synthesis of both enantiomers of pericoxide via 6-bromopericosine A was also developed. These 6-halo-substituted pericosine A derivatives were evaluated in terms of their antitumor activity against three types of tumor cells (p388, L1210, and HL-60) and glycosidase inhibitory activity. The bromo- and iodo-congeners exhibited moderate antitumor activity similar to pericosine A against the three types of tumor cell lines studied. The fluorinated compound was less active than the others, including pericosine A. In the antitumor assay, no significant difference in potency between the enantiomers was observed for any of the halogenated compounds. Meanwhile, the (−)-6-fluoro- and (−)-6-bromo-congeners inhibited α-glucosidase to a greater extent than those of their corresponding (+)-enantiomers, whereas (+)-iodopericosine A showed increased activity when compared to its (−)-enantiomer

Synthesis of Natural O-Linked Carba-Disaccharides, (+)- and (−)-Pericosine E, and Their Analogues as α-Glucosidase Inhibitors

Pericosine E (6), a metabolite of Periconia byssoides OUPS-N133 was originally isolated from the sea hare Aplysia kurodai, which exists as an enantiomeric mixture in nature. The enantiospecific syntheses of both enantiomers of Periconia byssoides OUPS-N133 has been achieved, along with six stereoisomers, using a common simple synthetic strategy. For these efficient syntheses, highly regio- and steroselective processes for the preparation of bromohydrin and anti-epoxide intermediates were applied. In order to access the unique O-linked carbadisaccharide structure, coupling of chlorohydrin as a donor and anti-epoxide as an acceptor was achieved using catalytic BF3·Et2O. Most of the synthesized compounds exhibited selectively significant inhibitory activity against α-glycosidase derived from yeast. The strongest analog showed almost 50 times the activity of the positive control, deoxynojirimycin

Synthesis of Marine Natural Product (−)-Pericosine E

The first synthesis of (−)-pericosine E (<b>6</b>), a metabolite of the Periconia byssoides OUPS-N133 isolated originally from the sea hare Aplysia kurodai, has been achieved. Efficient and regio­selective synthetic procedures for the synthesis of key intermediates, <i>anti-</i> and <i>syn-</i>epoxides <b>9</b> and <b>10</b>, were developed using an <i>anti</i>-epoxidation of diene <b>12</b> with TFDO and a bromo­hydrination of <b>12</b> with NBS in CH₃CN/H₂O (2:3), respectively. In addition, comparison of the specific optical rotations between synthetic <b>6</b> and natural <b>6</b> elucidated that the naturally preferred enantiomer of pericosine E had the same absolute configuration as (−)-<b>6</b> synthesized from chloro­hydrin (−)-<b>8</b> and <i>anti</i>-epoxide (+)-<b>9</b>

Mannose-Binding Lectin Inhibits the Motility of Pathogenic <i>Salmonella</i> by Affecting the Driving Forces of Motility and the Chemotactic Response

<div><p>Mannose-binding lectin (MBL) is a key pattern recognition molecule in the lectin pathway of the complement system, an important component of innate immunity. MBL functions as an opsonin which enhances the sequential immune process such as phagocytosis. We here report an inhibitory effect of MBL on the motility of pathogenic bacteria, which occurs by affecting the energy source required for motility and the signaling pathway of chemotaxis. When <i>Salmonella</i> cells were treated with a physiological concentration of MBL, their motile fraction and free-swimming speed decreased. Rotation assays of a single flagellum showed that the flagellar rotation rate was significantly reduced by the addition of MBL. Measurements of the intracellular pH and membrane potential revealed that MBL affected a driving force for the <i>Salmonella</i> flagellum, the electrochemical potential difference of protons. We also found that MBL treatment increased the reversal frequency of <i>Salmonella</i> flagellar rotation, which interfered with the relative positive chemotaxis toward an attractive substrate. We thus propose that the motility inhibition effect of MBL may be secondarily involved in the attack against pathogens, potentially facilitating the primary role of MBL in the complement system.</p></div

Chemotaxis assay of <i>Salmonella</i>.

<p>(a) Schematic presentation of the flow chamber used in the microscopic agar drop assay. (b) An attractive response of <i>Salmonella</i> to the agar drop containing 10 mM serine. Squares and triangles represent the results obtained in the presence and absence of MBL, respectively. The values represent the ratios of the number of cells near the agar drop at each time point relative to that at 0 min, immediately after starting the assay. Data are the average values of four independent experiments. Vertical lines are the standard deviation and the statistical analysis (the Student’s <i>t</i>-test) was preformed to evaluate the significance of the difference from the results of the control (*<i>P</i> < 0.05, **<i>P</i> < 0.01).</p

Motility of <i>Salmonella</i> was affected by the addition of MBL.

<p>(a) Swimming fraction. More than 100 cells were analyzed 30 min after starting an experiment. The average values of three independent experiments are shown. The agglutination was observed under the microscope and evaluated as shown in parenthesis as follows: −, no agglutination; +, partially agglutinated but some cells displaying motility; ++, completely agglutinated (b) Time course of the swimming speed measured in the presence of 2.5 μg/ml MBL. The time displayed on the horizontal axis is one after the addition of MBL. Rectangles and triangles represent MBL-treated cells and the control group, respectively. The average values of more than 100 cells are shown. Vertical lines denote the standard deviation. Statistical analysis (the Student’s <i>t</i>-test) was performed to evaluate the significance of the difference from the data of the control at each concentration (*<i>P</i> < 0.05, **<i>P</i> < 0.01).</p

Effect of MBL on single flagellar rotation in wild-type <i>Salmonella</i>.

<p>(a) Schematic representation of the tethered cell assay. Typical results obtained from independent cells in motility buffer in the absence (b) and presence (c) of MBL are shown. The positive and negative values indicate counterclockwise (CCW) and clockwise (CW) rotations, respectively. (d) Ratio of CW to CCW rotations. Values are the average of 25 flagellar motors. Vertical lines denote the standard deviation. (e) Average rotation rates of <i>Salmonella</i> flagella measured 30 min after the addition of MBL to the motility medium. The data are the average values of 21 cells obtained in three independent trials. Vertical lines denote the standard deviation, and asterisks indicate the results of statistical analysis (*<i>P</i> < 0.05).</p

Effect of MBL on the fluorescence intensity of DiBAC₄(3).

<p>An increase in fluorescent intensity corresponds to a decrease in membrane potential. Fluorescent intensities at 517 nm obtained by excitation at 495 nm were determined using a fluorescence plate reader. The values are relative to the fluorescent intensity obtained in the motility buffer without MBL (−MBL). The average values of triplicate experiments are shown. Vertical lines are the standard deviation. The Student <i>t</i>-test was performed to indicate a significant difference between the results of −MBL and +MBL (*<i>P</i> < 0.05).</p