Diterpenoide Drüsenfarbstoffe aus Labiaten: 3β‐Acetoxyfuerstion, Nilgherron A und Nilgherron B, neue Chinomethane aus <i>Plectranthus nilgherricus</i> B<scp>ENTH</scp>.; absolute Konfiguration von Fuerstion

Abstract

Leaf‐gland Pigments: 3β‐Acetoxyfuerstione, Nilgherron A and Nilgherron B, New Quinomethanes from Plectranthus nilgherricus B ENTH . ( Labiatae ); Absolute Configuration of Fuerstione We have isolated from leaf‐glands of the above mentioned plant the following deeply coloured quino‐methane derivatives: (1) traces of the already known fuerstione ( 1a ); 11,15‐dihydroxy‐5,7,9 (11), 13‐abietatetraen‐12‐one; (2) the new 3β‐acetoxy‐fuerstione ( 1b ); (3) nilgherron A ( 5a , I or II), a new dimeric diterpenoid quinomethane, C 40 H 52 O 7 , formed in the plant obviously by cycloaddition of the o ‐quinone 8 (9a S , 11 R )‐11 ‐hydroxy‐2‐(1‐hydroxy‐1‐methylethyl‐9,9‐dimethyl‐3,4,7,8,9,9a,10,11‐ octahydro‐5 H ‐dibenzo [ a , d ]cycloheptene‐3,4‐dione) with fuerstione; (4) nilgherron B ( 5b , I or II), C 42 H 54 O 9 , likewise a new compound, formed by the same type of cycloaddition (heterodiene synthesis) of 8 with 3β‐acetoxyfuerstione. On the basis of 1 H‐NMR. shift arguments structure I is slightly preferred to II for 5a and 5b . Model experiments have shown the easy formation of the dihydrodioxin ring by reaction of an o ‐benzoquinone with p ‐quinomethanes. The absolute configuration of fuerstione and 3β‐acetoxyfuerstione has been determined by chiroptical methods.