The chemistry and morphology of Vepris wadigo (Rutaceae) a new Endangered tree of Kenyan coastal forest with the description of wadigin, a newly named alkaloid.

Abstract

Here we describe Vepris wadigo based on new collections and observations of the informally published Diphasia sp. A of the Flora of Tropical East Africa. Vepris wadigo is known with certainty only from Kaya Kinondo and Kaya Timbwa forests in Kwale District of coastal Kenya where it is known as Mchikoma (Digo language). A sterile specimen from the Usambara Mts of Tanzania suggests that the species may also occur there, but this needs verification with a fertile specimen. Vepris wadigo is compared with the only other known diphasoid Vepris species of East Africa, Vepris morogoroensis of Tanzania. However, Vepris wadigo most closely resembles Vepris stolzii of Tanzania which differs in the 4-locular fruit. The chemistry of Vepris wadigo is unique among the African species of Vepris which have been analysed, since acridones, quinolines and limonoids which characterise the genus were not detected. The six compounds which were characterised included compound 1 a benzamide newly described and named in this paper as wadigin (N-(2,6-dihydroxybenzoyl)-O-methyltyramine) which is an O-glucosylated derivative of riparin III, and four lignans and neolignans not previously found or very unusual in Vepris, namely heterotropan (2), asaraldehyde (3) a degradation product of compound 4, E-asarone (4) and its isomer, Z- asarone (5). Finally, Lupeol (compound 6) which has previously been found in African Vepris. Vepris wadigo is here provisionally assessed as Endangered, EN B1ab(i-iii)+B2ab(i-iii) since only two threat-based locations are known, with an area of occupation of 8 km2 using the IUCN preferred 4 km2 cell size, although the actual total area of the habitat occupied is 22.57 Ha as calculated with Google Earth Pro. Since there are only two points the extent of occurrence cannot be calculated. Satellite imagery has shown that the area of the habitat has slowly decreased in recent decades.