Candidate herbicide

Our systematic optimization approach from a sound basic research idea to create field-test candidate herbicide provided valuable information on chemistry and biology of alkylphosphonates. Our research confirmed that plant PDHc El could be a new target for herbicide R/D. We hope that our biorational design in the synthesis of the alkylphosphonates as plant PDHc El inhibiters, paved the way for other biorational designs to find new pesticides with novel mode of action in the future. 

Because ideal candidates for commercially-viable herbicides should have both strong phytotoxicity to susceptible weeds and low mammalian... 

The broad spectrum of biological activities, including insecticidal and herbicidal applications, of diverse molecular species containing the oxime function is discussed in several reviews published between 2001 and 2005 by Abele and colleagues . Many of these oximes are potential candidates for drugs with a number of applications as outlined in the following. 

Within a short time, the discovery of and screening for the herbicidal properties of dialkylamino-.v-triazincs led to selection of the most promising candidates for field development and eventual commercial use. 

These two chemicals were among 35 active derivatives selected for further evaluation in the held in order to differentiate between the various compounds, establish a complete and accurate prohle for each, and separate the promising ones from less than superior candidates with respect to their potential as commercial herbicides. Between the various triazine analogs, several were found to be identical in some biological characteristics. With many on-farm successes or failures dependent on the decision, each test and minute observation or difference was of critical importance. So the testing of four test plants (oat, mustard, cucumber, and onion) was expanded to nine, adding sugar beet, corn,... 

This table includes all candidates that were at least in the field development stage between 1952 and 1968. Chemical names, structures, and properties of these and all other triazine herbicides and many metabolites are also given in Appendix in Tables 1, 2 and 3. 

Methylthio-v-triazine group candidates reaching the herbicide market were the following ... 

G-32911, simetryn Simetryn was one of the first methylthiotriazine candidates tested, but was developed slowly until it was confirmed that rice had a higher crop tolerance to simetryn than to prometryn. It found its commercial place in the transplanted rice of Japan and in other countries in the subtropical rice belt. Simetryn is used to control broadleaf weeds in mixtures with other herbicides that are active against grasses. 

Terbutryn soon found markets in various crops and occupied important niches. Mixtures of low rates of terbutryn with near normal rates of atrazine have been used. Further opportunities for terbutryn were found in pea, broad bean (Viciafaba L. var major (Harz.)), common vetch, potato (always in mixture with simazine, or later with terbuthylazine), and sunflower, as well as grain sorghum and sugarcane in special situations. Terbutryn was the last candidate to reach the market during the first 15 years of the herbicide project. 

Drug candidates have also been derived from herbicides and fungicides. By screening the BASF library for endothelin receptor ligands, compound 96 was... 

Synthetic Herbicides. Most commercial phytotoxins (herbicides) have been discovered through random screening programs, followed by derivative synthesis and activity studies when a potential chemical candidate Is discovered. Seldom has a bloratlonal approach for herbicide discovery been achieved or used. Over the past 4S-50 years, perhaps close to a million compounds have been screened for herbicldal activity. The number of compounds screened has continually Increased and estimates for the 1980 s suggest that 12 to 15 thousand compounds per year were synthesized and screened for each compound reaching the market (28). In the 1990 s, the ratio may Increase 5-fo1d. 

The concept of integrating a chemical herbicide and a microbial herbicide to control a target weed can be illustrated by the example of waterhyacinth, Eichornia crasaipes. The microbial herbicide candidate, Cercospora rodmanii, and sublethal rates of diquat or 3,4-D (0.3% and 6.4% respectively, of the current label rates) can be combined to achieve a better control of waterhyacinth than is possible with the microbial herbicide alone (Charudattan 1985, unpublished data). In this case, the integration is intended primarily to inqprove the efficacy of the microbial herbicide (5). 

One possible approach to developing new herbicides is to screen candidate molecules against both resistant and susceptible weeds, or the resistant and susceptible target enzymes from these weeds. This approach was used to identify novel ACCase inhibitors that inhibited the target enzyme from a collection of resistant and susceptible biotypes... 

Carlson D. L. and Roberts A. L. (2002) Acid-and base-catalyzed hydrolysis of chloroacetamide herbicides. Amer. Chem. Soc., Div. Environ. Chem., Nat. Meeting, Symposium on Chemistry of EPA Contaminant Candidate List Compotmds, presented August, 2002, Boston, MA. 

We have found that several new fluorinated herbicide candidates currently under investigation at Monsanto are very efficient at electron capture and thus are ideally suited for negative ion LC/MS. One such candidate is the pre-emergence herbicide dithiopyr 1 which is illustrated in Figure 1. Dithiopyr is representative of a novel class of fluorinated pyridine herbicides whose metabolism has been studied extensively by negative ion LC/MS. 

Preparation of urine samples. Urine was collected from Fischer 344 rats eight hours after dosing with the herbicide candidate. The urine was kept frozen until mass spectral analysis. After thawing, the urine was centrifuged for two minutes at 13,600 g before injection onto the liquid chromatograph. 

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