We report that N(2),N(6)-bis(4-nitrophenyl)pyridine-2,6-dicarboxamide, which is related to known isophthalic acid dianilides, transports Cl(-) ions through phospholipid bilayer membranes and shows clear evidence of channel activity.

Three known alkaloids, isoboldine (2), norisoboldine (1), and magnoflorine (8), have been isolated for the first time from Croton lechleri, a source of the wound healing latex "sangre de grado". An HPLC system was developed, and a large number of latex and leaf samples of C. lechleri from 22 sites in northern Peru and Ecuador were analyzed to gain an understanding of the natural variation in alkaloid content for the species. Up to six alkaloids were found to occur in the leaves including, in addition to those listed above, thaliporphine (3), glaucine (4), and taspine (9), whereas the latex contained only 9. Taspine (9) is the component that has been previously found to be responsible for the wound healing activity of C. lechleri latex, and its mean concentration throughout the range examined was found to be 9% of the latex by dry weight. In addition, three chemotypes are defined based on the alkaloid content of the leaves, and the geographic distribution of these chemotypes is discussed along with a quantitative analysis of the alkaloid content as a function of chemotype.

Six amphiphilic heptapeptides with the structure (C 18 H 37 ) 2 NCO-CH 2 OCH 2 CO-(Gly) 3 -Pro-(Gly) n -(Glx)-(Gly) m -O(CH 2 ) 6 CH 3 , in which Glx represents glutamic acid or its benzyl ester and n+m=2, have been studied. In addition, the glutamate residue in the GGGPGGE sequence was esterified by fluorescent 1-pyrenemethanol. These compounds insert into phospholipid bilayers and form anionconducting pores. Hill plots based on carboxyfluorescein release indicate that the pores are at least dimeric. Studies that involved ion-selective electrode techniques showed that transport of chloride varied with the position of glutamate within the peptide chain and whether glutamic acid was present as the free acid or its benzyl ester. Chloride transport activity was significantly higher for the glutamate esters than for free carboxylates irrespective of the glutamate position. Activity was highest when the glutamate residue in ∼(Gly) 3 -Pro-(Xxx) 3 ∼ was closest to the C terminus of the peptide. A fluorescent pyrene residue was introduced to probe the aggregation state of the amphiphile. The selectivity of the pore for Cl -over K + was maintained even when the carboxylate anion was present within it. Complexation of Cl -by the ionophoric peptides was confirmed by negative ion mass spectrometry. Planar bilayer voltage clamp experiments confirmed that pores with more than one conductance state may form in these dynamic, self-assembled pores.

Aus dem sterischen Verlauf und aus der Geschwindigkeit der thermischen lsomerisierung von Cyclobutenen zu Butadienen folgt ein grundsatzlicher Unter- Es ist eine lang bekannte Eigenschaft aller Cyclobutene, sich thermisch zu Butadienen m isornerisieren1). Die Reaktion ist eines der einfachsten Beispiele fur eine Valenzisomerisierung und scheint auf den ersten Blick problemlos zu sein, da eine zu einer Doppelbindung auf zwei Wegen allylstiindige Einfachbindung gemal3 der Regel von STAUDINGER-SCHMIDT 2) geoffnet wird.Da wir bei unseren Arbeiten uber Versuche zur Darstellung eines Cyclobutadiens zahlreiche mono-, bi-und tricyclische Cyclobutene in die Hand bekamen, lag es nahe, deren Valenzisomerisierung naher zu studieren31. A. VALENZlSOMERlSlERUNG MONOCYCLISCHER CYCLOBUTENE

Seven synthetic anion transporters (SAT) of the general form R 2 N-COCH 2 OCH 2 CO-(Gly) 3 -Pro-(Gly) 3 -OR' were prepared. Three pairs of compounds each contained twin n-hexyl, n-decyl, and noctadecyl (R) groups at the N-terminus and one contained twin n-tetradecyl groups. Three of the compounds were C-terminated by benzyl and three by heptyl (R') residues. The ability of these compounds to mediate ion release from phospholipid vesicles was assessed. Chloride release was measured by ion selective electrode measurements and by chloride quenching of the fluorescent dye lucigenin. Transport of the anion carboxyfluorescein (CF) was measured by fluorescence dequenching. Differences in both the C-(R') and N-terminal (R) residues within the ionophores affected anion transport. The chloride release data acquired by ion selective electrode and fluorescence methods were similar but not identical. A possible carrier mechanism for Cl -transport was discredited. Both Cl -and CF anions were released from vesicles by these compounds. The results of CF and Cl -transport showed good consistency when the ionophore's N-terminal chains were either decyl or octadecyl but not when they were hexyl. The transport of CF and Cl -appears to be fundamentally different when R is C 6 compared to C 10 or C 18 . Differences between the behavior of SATs with Cl -and CF were also reflected in negative ion mass spectrometric studies.

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NHMe 3 ][7-Me-µ-(9,10-HMeC)-nido-7-CB 10 H 10 ] (1) reacts with [PdCl 2 (PPh 3 ) 2 ] in refluxing ethanol solutions to afford four compounds which are the result of PPh 3 addition. Three of the products are structural isomers, viz. [5-PPh 3 -7-Me-µ-(9,10-HMeC)-nido-7-CB 10 H 9 ] (2), [6-PPh 3 -7-Me-µ-(9,10-HMeC)-nido-7-CB 10 H 9 ] (3), and [2-Me-3-{CHMe(PPh 3 )}-closo-2-CB 10 H 9 ] (4), and the fourth is [7-Me-8-OEt-9-{CHMe(PPh 3 )}-nido-7-CB 10 H 10 ] (5). The compounds were characterized by NMR spectrometry, high-resolution mass spectrometry, and single-crystal X-ray diffraction studies and are the first derivatives of the "unreactive" [7-R-µ-(9,10-HRC)nido-7-CB 10 H 10 ]anion (R ) Me) not involving degradation.

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