6-Substituted-4-(3-bromophenylamino)quinazolines as putative irreversible inhibitors of the epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor (HER-2) tyrosine kinases with enhanced antitumor activity.

A series of new 6-substituted-4-(3-bromophenylamino)quinazoline derivatives that may function as irreversible inhibitors of epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor (HER-2) tyrosine kinases have been prepared. These inhibitors have, at the C-6 position, butynamide, crotonamide, and methacrylamide Michael acceptors bearing water-solublilizing substituents. These compounds were prepared by acylation of 6-amino-4-(3-bromophenylamino)quinazoline with unsaturated acid chlorides or mixed anhydrides. We show that attaching a basic functional group onto the Michael acceptor results in greater reactivity, due to intramolecular catalysis of the Michael addition and/or an inductive effect of the protonated basic group. This, along with improved water solubility, results in compounds with enhanced biological properties. We present molecular modeling and experimental evidence that these inhibitors interact covalently with the target enzymes. One compound, 16a, was shown to have excellent oral activity in a human epidermoid carcinoma (A431) xenograft model in nude mice.

Chiral recognition by CD-sensitive dimeric zinc porphyrin host. 2. Structural studies of host-guest complexes with chiral alcohol and monoamine conjugates.

A structural study of complexes formed between a dimeric zinc porphyrin tweezer (host) and chiral monoalcohols and monoamines derivatized by a bidentate carrier molecule (guest) confirmed that their CD couplets arise from the preferred porphyrin helicity of 1:1 host-guest complexes. NMR experiments and molecular modeling of selected tweezer complexes revealed that the preferred conformation is the one in which the L (larger) group protrudes from the porphyrin sandwich; this preferred helicity of the complex determines the CD of the complexes. It was found that the porphyrin ring-current induced (1)H chemical shifts and molecular modeling studies of the complex lead to the assignments of relative steric size of the L (large)/M (medium) substituents attached to the stereogenic center. The assignments, in turn, are correlated with the sign of the CD exciton couplet that establishes the absolute configuration at the stereogenic center. Variable-temperature NMR experiments proved that the observed increase in CD amplitude at lower temperatures derives from conformational changes in the preferred offset geometry between two porphyrin rings.

Antiproliferative and immunosuppressive properties of microcolin A, a marine-derived lipopeptide.

The immunosuppressive effects of microcolin A, a lipopeptide extracted from the marine blue green alga Lyngbya majuscula were investigated. Microcolin A suppressed concanavalin A (IC50 = 5.8 nM), phytohemagglutinin (IC50 = 12.5 nM) and lipopolysaccharide (IC50 = 8.0 nM) induced proliferation of murine splenocytes. Mixed lymphocyte reaction (IC50 = 5.0 nM), anti-IgM (mu-chain specific) (IC50 = 10.0 nM), and phorbol 12-myristate 13-acetate plus ionomycin (IC50 = 5.8 nM) stimulation of murine splenocytes were all similarly suppressed by microcolin A. The inhibitory activity of microcolin A was time-dependent and reversible and was not associated with a reduction in cell viability. Moreover, microcolin A not only inhibited IL-2 production and IL-2 receptor expression by concanavalin A activated splenocytes, but also suppressed in vitro antibody responsiveness to keyhole limpet hemocyanin. These results indicate that microcolin A is a potent immunosuppressive and antiproliferative agent.

Analogues of the marine immunosuppressant microcolin A: preparation and biological activity.

A series of analogs of the immunosuppressive lipopeptide microcolin A has been prepared and evaluated for in vitro activity in the human and murine two-way mixed lymphocyte reaction. The compounds tested were obtained by semisynthetic modification and chemical degradation of the natural product. The relative potencies of these analogs suggest that the hydroxyproline and 5-methyl-3-pyrrolin-2-one portion of the molecule are important for immunosuppressive activity and that other structural elements may play an ancillary role. Methanolysis of microcolin A also led to a novel immunosuppressive lactone analog.

Microcolins A and B, new immunosuppressive peptides from the blue-green alga Lyngbya majuscula.

Microcolin A [1] and microcolin B [2] are new immunosuppressive lipopeptides isolated from a Venezuelan sample of the blue-green alga Lyngbya majuscula. The microcolins are potent inhibitors of the murine mixed lymphocyte response and murine P-388 leukemia in vitro. Isolation and structure elucidation of 1 and 2 by nmr, mass spectral, and chemical methods are described.

Inaction of saxitoxin-oximes on the sodium channel of frog skeletal muscle fibers.

Three oximes of saxitoxin, saxitoxin oxime, saxitoxin methyloxime, and saxitoxin carboxymethyloxime, were synthesized in which the oxime functions replaced the ketone function on C-12 of saxitoxin. On the voltage-clamped single frog muscle fibers these oximes were very weak or inactive in blocking the sodium channel. The results indicate that the hydrated ketone function in saxitoxin is essential for blockade of the sodium channel, probably through a hydrogen bonding mechanism with some receptor groups.

Actions of epimers of 12-(OH)-reduced saxitoxin and of 11-(OSO3)-saxitoxin on squid axon.

The actions of the 12 alpha-saxitoxinol, 12 beta-saxitoxinol and a C-12 ethylene thioketal derivative of saxitoxin, as well as those of 11 alpha-(OSO3)-saxitoxin, 11 beta-(OSO3)-saxitoxin and 11 alpha-(OH)-saxitoxin, have been examined on the isolated squid giant axon. Each of these analogues acted similarly to saxitoxin in blocking specifically the sodium channel. The relative potencies are: STX (1); 11 beta-(OSO3)-STX (gonyautoxin III) (0.42); 11 alpha-(OSO3)-STX (gonyautoxin II) (0.20); 11 alpha-(OH)-STX (0.10); 12 alpha-saxitoxinol (0.0021); 12 beta-saxitoxinol (0.0005). Thus, the presence of a bulky and negatively charged sulphate group on C-11 does not materially affect the biological activity of STX. Hydrogen bonding at the C-12 position is probably an important means of binding of STX to the membrane receptor site. The difference between the epimers of saxitoxinol suggests that the H in one of them may be geometrically better aligned than that in the other, with the hydrogen acceptor group in the receptor.