Sir:1n the course of our studies on the plant growth regulators in marine algae, we found the existence of auxin-like substances which promote the growth of A vena coleoptile sections in Ulva pertusa Kjellman The young thalli (118 kg) of Undaria pinnatifida were collected in February at Aburatsubo on the coast of the Sagami Bay that were washed with water and cut into small pieces and extracted twice with methanol. After evaporation of the solvent, the aqueous residue was separated by the usual method to afford an ethyl acetate-soluble strong acid fraction. The acidic material (5.9 g) was dissolved in acetonitrile and washed with nhexane. After the acetonitrile layer was evaporated to dryness in vaccuo, the dry material was subjected to a counter-currentdistribution of 9 transfers between etheyl acetate (450 ml) and phosphate buffer (pH 6.65, 450 ml). The active substances were recovered from tube numbers 2-6. The combined fraction was further purified by partition chromatography using silicic acid (stationary phase: phosphate buffer, pH Native Auxins in Marine Algae 6.65; mobile phase: ethyl acetate-hexane). The active fraction which was eluated from the column with ethyl acetate (8-10 %)-hexane mixture gave finally ca. 1 mg of substance A (active) and ca. 0.5 mg of substance B (inactive) after repeated purification by preparative TLC (Kiesel Gel G and Avice! SF) (tentative name A and B show in Table I). Furthermore only a trace amount of another Ehrlich-positve substance was eluated with ethyl acetate (50 %)-hexane. Thus, approximately 10 fig of auxins were yielded from 1 kg of fresh weight of the algae. This content was one-tenth less than that of higher plants.The UV absorption spectrum of A showed (Table I). Final identification was carried out by the analyses of the mass spectra of their methyl esters which were in agreement with those of their authentic specimens. Namely, the stepwise de-

A number of related 1,3,4-thiadiazole derivatives have been synthesized and their herbicidal activities have been evaluated by pre-emergence, postemergence, and irrigated water treatment methods. Some l-substituted-3-(5-substituted-l,3,4-thiadiazol-2-yl)ureas showed excellent herbicidal activity. This activity depends upon the molecular size of the substituent in the 5-position of 1,3,4-thiadiazole ring. In particular, activity is maximized when the substituent is the tertiary-butyl group, while replacement of the O atom in the urea moiety with a S atom resulted in decreased herbicidal activity. Further correlations of chemical structure to herbicidal activity are discussed.

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