Ruminations regarding the design of small mixtures for biological testing.

Synthesis and screening of compound mixtures offer avenues to increase throughput and reduce cycle time in the discovery of new drugs and agrochemicals. Equations are derived which show that the efficiency of synthesis and screening of mixtures is a function of the screening hit rate and the number of compounds in each mixture when simple one-step deconvolution by retesting the individual compounds in each active mixture is employed. Values of hit rate and number of compounds in each mixture which afford various levels of increased efficiency are delineated. Two-step deconvolution, in which the active mixtures from the first round of testing are subdivided into mixtures with fewer compounds for a second round of mixture screening prior to final testing of individual compounds, is shown to be more efficient than simple one-step deconvolution under most conditions. For optimum efficiency, the number of compounds in each mixture in the second round testing should be the square root of the number of compounds in each mixture in the first round. At high hit rates the efficiency of the double scan or indexed approach to deconvolution is shown to be higher than that of simple deconvolution. This discussion is oriented mainly toward mixtures of 4-20 compounds and screens which give hit rates in the 1-10% range. The equations describing efficiency are applied in the context of a 49-member amide library produced as mixtures of seven compounds. This library includes the commercial herbicide pronamide and was screened for herbicidal and insecticidal utility.

Solid phase vs. solution phase differential behavior: formation of a salicylate structure from a malondialdehyde moiety.

Treatment of 2, solid supported synthetic equivalent of 3-formylchromone (4), and ethyl acetoacetate affords the salicylate structure 8 instead of the previously reported isophtalate 7. This is the first formation of a salicylate by a double carbonyl condensation of a malondialdehyde moiety ever reported.

Antifungal properties of taxol and various analogues.

The antimitotic agent taxol was tested for toxicity towards fungi from different taxonomic groups and found to be particularly active against oomycete fungi. In germinating zoospore cysts of the oomycete Phytophthora capsici the mechanism of action of taxol was shown to involve inhibition of mitosis, presumably resulting from an effect on microtubules. Various taxol analogues with deleted A-ring C-13 side chain substituents were tested for toxicity towards P. capsici and Aphanomyces cochlioides to provide insight into structural features required for activity. The importance of the side chain was shown by the much lower activity as compared to taxol of analogues lacking all or part of the side chain. The effect of stereochemistry at the C-2' position on fungitoxicity towards oomycetes was similar to that reported previously on mammalian microtubule assembly.

Effect of side-chain shortening on the physiologic properties of bile acids: hepatic transport and effect on biliary secretion of 23-nor-ursodeoxycholate in rodents.

To define whether side-chain length influences the physiologic properties of bile acids, nor-ursodeoxycholate (nor-UDC), the C23-nor derivative of ursodeoxycholate (UDC), was synthesized in both nonradioactive and radioactive forms (23-14C). Its hepatic translocation, hepatic biotransformation, and effect on bile flow, biliary bicarbonate, and biliary lipid secretion were compared with that of UDC and those of their respective glycine and taurine conjugates in anesthetized biliary fistula hamsters, rats, and guinea pigs, as well as the isolated perfused hamster liver. Hepatic uptake and biliary output of nor-UDC was slower than that of UDC or cholyltaurine in the isolated perfused hamster liver. In biliary fistula animals, nor-UDC was secreted only in bile. Biliary recovery of nor-UDC as compared to that of UDC was prolonged in the rat and hamster, although not in the guinea pig. Hepatic biotransformation, assessed by chromatography of bile, showed that conjugation of nor-UDC was inefficient, as unconjugated nor-UDC was present in bile; there was little amidation with glycine or taurine in any species, but sulfates and glucuronides, as well as other metabolites, were formed, with the pattern of biotransformation varying among species. When infused over a dosage range of 0.2-30 mumol/kg X min, nor-UDC induced a striking choleresis of canalicular origin. The bile acid-dependent flow was increased threefold in hamsters, ninefold in rats, and nearly twofold in guinea pigs when compared to that induced by UDC. The choleresis was associated with a linear increase in bicarbonate output and concentration in bile, and little phospholipid or cholesterol secretion was induced. A competition experiment in the bile fistula hamster indicated that nor-UDC or its metabolites, or both, appeared to compete for canalicular transport of ursocholyltaurine (a cholyltaurine epimer) when the latter was secreted under its Vmax conditions. Conjugates of nor-UDC and UDC were promptly and almost completely recovered in bile without appreciable hepatic biotransformation; the conjugates did not induce a hypercholeresis or increase biliary bicarbonate concentration. It is proposed that a fraction of nor-UDC is secreted into canalicular bile in the unconjugated form and is protonated by a hydrogen ion derived from carbonic acid that was generated by the hydration of luminal CO2 by carbonic anhydrase present in biliary ductular cells. The protonated bile acid is absorbed, thus generating a bicarbonate anion. The bile acid passes through the cholangiocyte, returns to the sinusoids via the periductular capillary plexus, and is resecreted into bile.(ABSTRACT TRUNCATED AT 400 WORDS)

Synthesis of a sulfahydantoin library.

A five-step solid-phase synthesis of sulfahydantoins from alpha-amino acids and aldehydes was developed. The synthetic method allows the use of hindered amino acids, including Val, Phg, and Aib, and use of aromatic aldehydes substituted with electron-withdrawing and -donating groups. Some limitations were encountered with amino acids with reactive side chains. A small but diverse library of compounds was produced for biological testing.

Structure-activity relationships of phenylcyclohexene and biphenyl antitubulin compounds against plant and mammalian cells.

Phenylcyclohexenes (PCHs) [e.g., trans-4-nitro-5-(2,3,4-trimethoxyphenyl)cyclohexene, 2d] were found to bind weakly to the colchicine site of bovine tubulin, but are the first mimics of colchicine found to have high activity towards plant cells. Structure-activity relationships for PCHs and biphenyl AC-ring analogues of colchicine (e.g., 2,3,4,4'-tetramethoxy-2'-methyl-1,1'-biphenyl, 3e) are discussed.