NOMENCLATURE

Common name oxasulfuron (BSI, pa ISO)

IUPAC name oxetan-3-yl 2-[(4,6-dimethylpyrimidin-2-yl)-carbamoylsulfamoyl]benzoate 

Chemical Abstracts name 3-oxetanyl 2-[[[[(4,6-dimethyl-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoate 

CAS RN [144651-06-9]  Development codes CGA-277476 (Ciba-Geigy) 

PHYSICAL CHEMISTRY

Mol. wt. 406.4  M.f. C₁₇H₁₈N₄O₆S  Form White, odourless powder.  M.p. 158 °C (decomp.)  V.p. <2 ´ 10^-3 mPa (25 °C)  K_OW logP = 0.75 (pH 5), -0.81 (pH 7), -2.2 (pH 8.9)  Henry <3.2 ´ 10^-5 Pa m³ mol^-1 (calc.)  S.g./density 1.41  Solubility In water 52 ppm (pH 5.1, 25 °C); in buffer, 63 (pH 5.0), 1700 (pH 6.8), 19 000 (pH 7.8) mg/l (15 °C). In methanol 1500, acetone 9300, toluene 320, n-octanol 99, n-hexane 2.2, ethyl acetate 2300, dichloromethane 6900 (all in mg/l, 25 °C).  pKa 5.1 

APPLICATIONS

Biochemistry Branched chain amino acid synthesis (ALS or AHAS) inhibitor. Acts by inhibiting biosynthesis of the essential amino acids valine and isoleucine, hence stopping cell division and plant growth. Selectivity derives from rapid metabolism in the crop. Metabolic basis of selectivity in sulfonylureas reviewed (M. K. Koeppe & H. M. Brown, Agro-Food-Industry, 6, 9-14 (1995)).  Mode of action Readily taken up by shoots and roots and translocated to meristematic tissues. Leaves turn yellow or red, followed by death after 1 to 3 weeks.  Uses Under development for broad-leaved and grass weed control in soya beans, at 60-90 g/ha.  Formulation types WG.

Methods for sulfonylurea residues in crops, soil and water reviewed (A. C. Barefoot et al., Proc. Br. Crop Prot. Conf. - Weeds, 1995, 2, 707). 

MAMMALIAN TOXICOLOGY

Oral Acute oral LD₅₀ for rats >5000 mg/kg.  Skin and eye Acute percutaneous LD₅₀ for rabbits >2000 mg/kg. No skin or eye irritation (rabbits). Not a skin sensitiser (guinea pigs).  Inhalation LC₅₀ for rats >5.08 mg/l air.  NOEL (2 y) for rats 8.3 mg/kg b.w. daily; (18 mo) for mice 1.5 mg/kg b.w. daily; (1 y) for dogs 1.3 mg/kg b.w. daily.  ADI 0.013 mg/kg b.w.  Other Non-mutagenic.  Toxicity class WHO (a.i.) III (Table 5) 

ECOTOXICOLOGY

Birds Acute oral LD₅₀ for quail and mallard ducks >2250 mg/kg. Dietary LC₅₀ for quail and mallard ducks >5620 ppm.  Fish LC₅₀ for bluegill sunfish >111, trout >116 mg/l.  Daphnia EC₅₀ (48 h) >89.4 mg/l.  Algae EC₅₀ for Selenastrum capricornutum 0.145, Navicula >20 mg/l.  Bees LD₅₀ >25 mg/bee.  Worms LC₅₀ for earthworms >1000 mg/kg. 

ENVIRONMENTAL FATE

Animals The majority (70-80%) of the applied dose is excreted in urine with no accumulation in tissues; depletion t_½ c. 7-14 h. The metabolic route involves hydroxylation of the pyrimidine methyl, hydrolysis of the oxetane ring and cleavage of the sulfonylurea bridge.  Plants The major metabolite is saccharine (0.002 ppm in mature beans); small amounts of oxetane alcohol are also formed. Metabolism follows a similar route to animals.  Soil/Environment Soil DT₅₀ (lab.) 10 d, (field) <2 w. Breakdown is primarily microbial and hydrolytic; independent of soil pH, organic matter content or soil structure. K_oc 44 (13 soils).