Methoprene acid

Exposure of juvenile insects to methoprene results in various abnormalities associated with development and ultimately death. The environmental degradation product of methoprene, methoprenic acid was found to serve as an RXR agonist and specifically activate genes responsive to RXR homodimers. In addition exposure of frog larvae to methoprenic acid caused developmental deformities consistent with those that have been observed in recent years in wild populations and consistent with those caused by exposure to retinoic acid under laboratory conditions. These observations indicate that methoprenic acid functions as an RXR agonist, and that this activity could contribute to the occurrence of amphibians deformities documented in the environment. 

Figure 3. Synthesis of the protected four-carbon spacer group (Structure 9), followed by coupling to methoprene acid (Structure 11) which yielded Structure 12. Deprotection of compound 12 gave methoprene-spacer acid (Structure 13).

The adaptation of immunochemical methods for many classes of small compounds has made it possible to develop assays for pesticide residue detection. A cELISA was developed for methoprene, an analog of insect juvenile hormone. Because of its size, methoprene does not elicit an immune response by itself. However, by conjugating methoprene to a carrier protein it was made immunogenic in animals. A four-carbon spacer group was incorporated between methoprene and the carrier protein. The spacer was first coupled to methoprene acid by a series of protection/deprotection steps. 

Methoprene is an insect growth regulator and it is also used as an insecticide for cockroaches. The enantioselective isomerization of 7-methoxygeranylamine in the presence of [Rh((+)-BINAP)2]+ followed by acid hydrolysis provides the intermediate, 7-methoxycitronellal, in high yield with high optical purity (97%, 98% ee, Scheme 6).9 Alternatively, methoxylation of ( -citronellalenamine (98% ee) with methanol in the presence of 97% sulfuric acid followed by hydrolysis gives 7-methoxycitronellal in 79% yield without racemiza-tion (Scheme 6).9... 

The identity of methoprene photoproducts has been studied from aqueous emulsions, thin films on glass or silica gel, and in methanolic solution (Figures 3 and 4, 40). As a thin film (0.1 ym) on glass, the half-life of methoprene was about 6 hr. After 93% degradation of parent, more than 50 photoproducts were observed, only five of these present in 3% or higher yield 7-methoxycitronellic acid (4%), 7-methoxycitronellal (4%), the 4,5-epoxide of methoprene (6%), a C12 methyl ketone (3%), and 14C02 (6%). Similar products were encountered on photolysis of a 100 ppm aqueous emulsion of methoprene, except that methoxy-citronellal was isolated only as its dimethyl acetal (9% yield), a presumed artifact of work-up. In addition to the same products identified from thin film studies, at least forty-six other discrete products were detected, but not identified (40). 

Fall has studied the capability of fourteen species of microorganisms to grow on methoprene as sole carbon source. One of these organisms, Cladosporium resinae, was able to utilize methoprene as sole carbon source, while another. Pseudomonas citronellolis, was similarly able to utilize 7-methoxycitronellic acid. (41). 

Soil microorganisms degrade methoprene rapidly and extensively (27). The hydroxy ester was isolated as a minor metabolite over 50% of the applied dose was evolved as 1 C02. Radioactivity from [5-1 0]methoprene incorporated into the humic acid, fulvic acid, and humin fractions of soil. 

Retinoic Acid Receptor. Most of the biological effects of retinoids are mediated through the retinoic acid receptor (RAR) and the retinoid X receptor (RXR). Both all-/ran.s-retinoic acid and 9-d.v-rctinoic acid serve as agonists of RAR, while only 9-d.v-rctinoic acid functions as an agonist of RXR. The functional RAR exists as a heterodimer with RXR, while functional RXR exists as a homodimer. Methoprene is a juvenile hormone III analogue that mimics the activity of this insect hormone. 

The parent spacer, 4-hydroxybutanoic acid, spontaneously undergoes loss of water under acidic or basic conditions to give 4-butyrolactone. To prevent cyclization when the spacer is coupled to methoprene, both the hydroxyl and carboxyl functions had to be protected and selectively deprotected. The methods used are summarized in Figure 2. The protection/deprotection chemistry described was originally developed for use in the field of peptide synthesis. 

The first reading (A406) measured the amount of free dianion in the mixture. Hydroxide was then added to completely hydrolyze compound 16 to its acid (Figure 5, Structure 13) and the dianion, and a second reading was taken (A.qa(NaOH)). This determined the amount of dianion liberated by the hydrolysis of this activated ester of methoprene. The percent total ester in the crude mixture was calculated using Equation 1. 

Figure 4. Preparation of the methoprene immunogen (Structure 15) by two methods a. The NHS-ester of methoprene (Structure 14) was conjugated to human serum albumin (H2N-HSA) in organic/aqueous solution, b. A water soluble active ester of methoprene (Structure 16) was prepared by the DCC coupling of methoprene-spacer acid (Structure 13) with l-hydroxy-2-nitro-4-benzene sulfonate. Reaction of compound 16 with H2N-HSA was carried out in aqueous phosphate buffered saline (PBS).

Figure 5. Hydrolysis reaction of HNSA-ester (Structure 16) with base gave methoprene-spacer acid (Structure 13) and the dianion (Structure 17). The spectrum shows the absorbance of the dianion before ( ) and after hydrolysis (o).

This class of lipid conjugates Is the most nonpolar yet Identified, a characteristic which Is often useful In pursuing the Identification of unknown metabolites. The first cholesterol ester of a xenobiotic was reported In 1976 for a saturated methoprene metabolite which contributed 15% of the total C-resldue In the liver of a chicken given a single oral dose of methoprene at 64 mg/kg (17). The tai-cyc lop ropy 1 fatty acids derived from cycloprate also form esters of cholesterol. Three such esters contributed 5% of the total residual radiocarbon In rat carcasses four days after a single oral dose of cycloprate at 21 mg/kg ( ). 

Dodecadienoic acid. 11-nnethoxy-3.7.11-trimethyl-. 1-methylethyl ester, E.E)-(Kabat , Minex , Methoprene Altoside 1242,1243, 21A19 1242, 1243, 1588, 2483a, 3633. 21A19 ... 

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