STRUCTURE-ACTIVITY-RELATIONSHIPS IN ALLERGIC CONTACT-DERMATITIS .1. STUDIES ON THE INFLUENCE OF SIDE-CHAIN LENGTH WITH DERIVATIVES OF PRIMIN

Primin (2-methoxy-6-pentyl-1,4-benzoquinone:) is a naturally-occurring strong sensitizer from Primula obconica (Primulaceae). To determine t he effect of side-chain length on sensitizing potency, 15 analogues wi th linear side chains from C-1 to C-15 and 4 Cd-analogues with branche d side chains were prepared synthetically and devoted to experimental sensitization in guinea pigs. The results showed an increase of the se nsitizing capacity with increasing length of the alkyl side chain from C-1 to C-13 reaching a maximum at C-11 and C-12. On further elongatio n, the sensitizing potency decreased beyond C-13, reaching values whic h finally were as low as those of the C-1 and C-3 derivatives. The res ults mirror findings which formerly have been obtained with other non- quinonoid compounds like catechols, phenols, hydroquinones and gallate s. In the plant kingdom, compounds approximating an ''ideal allergen'' consisting of a quinonoid ring with a 10 or 11 carbon-membered side c hain have been identified only once: 2,3-dimethoxy-geranyl- 1,4-benzoq uinone, a remarkably strong sensitizer found in Wigandia caracasana (H ydrophyllaceae).