z z z 5 8 11 14 eicosatetraenoic and the like the preferred compounds of this invention are realized when the double bonds are all in a cis configuration further preferred compounds are realized when there is one double bond in the alkenyl group still further preferred compounds are realized when the alkenyl group contains from 16 to 20 carbon atoms the most preferred alkyl group contains 18 carbon atoms and is oleyl z 9 octadecene these compounds are prepared by reacting fluorescein with a reagent capable of alkylating the carboxylic acid as well as the phenolic hydroxyl groups common alkylating reagents known in the art for alkylating carboxylic acids and phenols were tried and found to be unsatisfactory the novel reagent o alkenyl n n 39 dialkylisourea ii was then prepared and this compound was found to successfully and simultaneously alkylate both the carboxylic acid and phenolic hydroxyls of fluorescein the structure of this reagent is str3 wherein r is as defined above and r 1 and r 2 are independently loweralkyl of from 1 to 6 carbon atoms or cycloalkyl of from 4 to 6 carbon atoms the loweralkyl groups may be either straight or branched chain the preferred compounds are those wherein r 1 and r 2 are the same further preferred compounds are when r 1 and r 2 are isopropyl or cyclohexyl the most preferred compounds is when r 1 and r 2 are isopropyl the novel reagent of this invention ii is prepared by reacting an n n 39 dialkyl carbodiimide iii with an alcohol iv as in the following reaction scheme str4 wherein r r 1 and r 2 are as defined above both starting.