Isolation and characterisation of guaianolides from Helichrysum montanum and H. splendidum

Abstract

The genus Helichrysum (Asteraceae) consists of approximately 500 species worldwide, with 245 species indigenous to South Africa [1].These plants are often used medicinally and are chemically diverse [2,3]. The aim of this study was to investigate the phytochemistry of H. montanum, a species morphologically closely related to H. splendidum, which is used traditionally to treat rheumatism [4]. An extract of H. montanum yielded four guaianolides, a flavonoid and a coumarin. The complex stereochemistry of the guaianolides presented a challenge during structure elucidation since several stereoisomers have been reported from other Helichrysum species and from other genera [3,5]. The guaianolides from H. splendidum were also reisolated and a crystal structure obtained for helisplendidilactone (a dimeric guaianolide, C30H40O5, monoclinic P21, a=9.0738(5), b=11.4764(7), c=12.2960(9) Å, β=96.933(5)°, Z=2, R 1=0.0516, T=100(2) K), which assisted in the structure elucidation of dimer 1 from H. montanum. The presence of the guaianolides is significant, since this type of compound is rare in this genus and also in the subtribe (Gnaphaliineae) [3].