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Strigol analogs

In preparation for scale-up of the strigol synthesis described by Sih (8), efforts were made to improve the yield of some of the seven steps involved in the scheme. Of these steps, nine are satisfactory from the standpoint of yield and experimental conditions. For three of the steps, we have improved the yield and/or experimental conditions such that the yield of (+ )-strigol would be raised to 2.85% overall from citral rather than 1.53% based on Sih s procedure and reported yields. Improvements were developed preparation of a-cyclocitral (III), the oxidation of the hydroxyaldehyde (V) to the ketoacid (VII), and for the preparation of the hydroxybutenolide (XVII). For the remaining five steps, our attempts to change experimental conditions have failed to improve, and in most cases to even obtain, the yields reported in the literature (8). We have considered the preparation of strigol analogs and determined the conditions and limitations for the preparation of a series of alkoxybutenolides (XVI) and a butenolide dimer (XVIII). Modification of the literature procedure (11) to eliminate the use of the mesylate (XX) and the use of polar aprotic solvents gave better yields of the 2-RAS (XXI). [Pg.425]

Most of the work on correlation of molecular structure with bioactivity in witchweed seed germination has been produced by two groups (7-10). Johnson, et al. (7-9) prepared and evaluated a large number of strigol analogs and many approached the activity of strigol. In many studies by others, the results of the bioassays are presented, but the compounds from Johnson are described only by GR-number. GR-7 and -24, probably the more promising of these compounds, have been used in extensive field studies, and their structures are known. [Pg.450]

Bioactivity of Strigol, Strigol Analogs., their Precursors, and Related Compounds—... [Pg.451]

Because of the lengthy periods of viability of the seeds of Stri ga and Orobanche (broomrape) in the soil, effective control of these parasitic weeds is extremely difficult. An attractive method of control would involve treatment of an infected field with a biosynthetic product (such as strigol) or synthetic analog to induce suicidal germination of the weed seed in the absence of a host plant. The results of field tests with ethylene (11) and synthetic strigol analogs (12) offer evidence of the utility of this method of control. [Pg.410]

Johnson s Syntheses of Strigol Analogs. The greatest volume of work in the preparation of synthetically simpler analogs of strigol has been performed by Johnson and coworkers (12,36-39) who have prepared two-, three-, and four-ring analogs. [Pg.426]

The strigol analogs prepared by Johnson and co-workers are normally obtained almost exclusively as the natural E-isomers. Each geometric isomer can exist as two diastereomers (39). Compounds 68 and 70 have been separated into their diastereoisomeric forms. In each case, the two diastereomers were almost equally active as germination stimulants (36). [Pg.428]

Other Syntheses of Strigol Analogs. In 1979, Cook and Co-workers reported the synthesis the aromatic analog 75 (42), which contains all but one of the carbon atoms of strigol. It was about 2% as active as strigol as a seed germination stimulant. The diastereomeric compound 76 exhibited one-hundredth of the activity of 75. [Pg.428]

A variety of strigol analogs have been synthesized and tested as germination stimulants with seeds of Striga and Orobanche (27-30). To provide a general overview, the structures and in vitro activity of some of the many compounds that have been evaluated are summarized in Scheme 3. The compounds 20-23 are early synthetic intermediates from the total synthesis of strigol and the hydroxy aldehyde 22 exhibits activity similar to strigol. [Pg.438]

The synthesis of strigol and its derivatives and the possibility of using these compounds for weed control and eradication has stimulated interest for their use in other parasitic and dormant weed seeds. A number of strigol analogs and precursors have been prepared and evaluated, permitting the proposal of structure-activity correlations. In this paper, we review these results and discuss the implications of these investigations. [Pg.446]

A limited amount of data on field-testing of strigol analogs has been reported, primarily involving GR-7 and GR-24. GR-7 was reported to be stable when incorporated in dry soil and to decompose slowly in wet soil (38). It was concluded that GR-7 was satisfactory for controlled stimulation of S. hermonthica in the African savanna. [Pg.458]

Pepperman AB, Bradow JM (1988) Strigol analogs as germination regulators in weed and crop seed. Weed Sci 36 719-725... [Pg.3603]

The literature preparation (11) of the two-ring analog of strigol (2-RAS) involved reacting the sodium enolate (XIX) with the mesylate (XX) to form 2-RAS (XXI). In our work we found it very difficult to prepare and purify the mesylate. Low yields of 2-RAS contaminated with XVIII resulted. [Pg.424]

Another two ring analog of strigol was prepared in a similar manner from the sodium enolate of a-valerolactone (XXII) and XIV. There is a methyl group at the 5-position of the ring which would correspond to the C-ring of strigol, so the shorthand for this compound is Me-2-RAS (XXIII). Johnson and co-workers (21) had... [Pg.424]

In addition, the elucidation of structure-activity relationships might provide a lead to the preparation of simpler analogs with biological activity. The use of synthetic intermediates encountered enroute to strigol can be used for the preparation of several analogs representing partial strigol structures. Our endeavors on this theme will be outlined. [Pg.437]

The synthetic studies which have been described have resulted in significant improvements in the preparation of racemic strigol and have also provided access to several analogs which will subsequently be tested for seed germination activity in order to elucidate key structure-activity relationships. These results and further investigations will hopefully lead to effective synthetic compounds for the control of witchweed and related parasitic plants. [Pg.443]

These reactions are highly selective for the desired IE isomer of strigol, its isomers, and analogs. It has been postulated ) that the isomer of the hydroxymethylene lactone is thermodynamically favored because it has the maximum separation of the negative oxygen centers. [Pg.450]


See other pages where Strigol analogs is mentioned: [Pg.416]    [Pg.417]    [Pg.443]    [Pg.449]    [Pg.453]    [Pg.455]    [Pg.425]    [Pg.438]    [Pg.448]    [Pg.449]    [Pg.3584]    [Pg.278]    [Pg.286]    [Pg.416]    [Pg.417]    [Pg.443]    [Pg.449]    [Pg.453]    [Pg.455]    [Pg.425]    [Pg.438]    [Pg.448]    [Pg.449]    [Pg.3584]    [Pg.278]    [Pg.286]    [Pg.416]    [Pg.417]    [Pg.418]    [Pg.422]    [Pg.422]    [Pg.424]    [Pg.426]    [Pg.434]    [Pg.437]    [Pg.437]    [Pg.442]    [Pg.442]    [Pg.445]    [Pg.446]    [Pg.449]    [Pg.449]    [Pg.450]    [Pg.450]    [Pg.10]    [Pg.158]    [Pg.159]   
See also in sourсe #XX -- [ Pg.451 , Pg.457 ]




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