Synthesis and bioactivity evaluation of brassinosteroid analogs

Four new analogs of 28-homocastasterone have been synthesized and completely characterized for the first time from stigmasterol. (22R, 23R,24S)-3beta-acetoxy-22,23-dihydroxy-5alpha-stigmastan+ ++-6-one (17), (22R,23R,24S)-3beta-bromo-22,23-dihydroxy-5alpha-stigmast an-6-one (18), (22R,23R,24S)-3beta-acetoxy-5,22, 23-trihydroxy-5alpha-stigmastan-6-one (20), and (22R,23R, 24S)-3beta-bromo-5,22,23-trihydroxy-5alpha-stigmastan-6-one (21), were obtained through a synthetic route based on regioselective Delta(5) epoxidation. Compounds 17 and 18, bearing a 5alphaH moiety, were prepared through a reductive opening of the 5beta,6beta epoxy precursor, and compounds 20 and 21, analogs with a 5alphaOH moiety were obtained by hydrolytic opening of a mixture of 5alpha,6alpha and 5beta,6beta epoxy precursors. Known compounds 19 and 22 were also obtained following the described synthetic routes, respectively. The new compounds were tested with the traditional auxin-like bioassay for brassinosteroids with 19 and 22 as standards. All compounds were comparatively evaluated for their inhibitory effect on the replication of DNA (HSV-1) virus.     

Identification of Potential Vectors and Alternative Plant Hosts for the Phytoplasma Associated with Napier Grass Stunt Disease in Ethiopia

Napier grass ( Pennisetum purpureum ), the most important forage crop in East Africa, has recently been affected by a devastating disease named Napier Grass Stunt (NGS). A phytoplasma of group 16SrI has been associated with NGS in Kenya and Uganda, whereas in Ethiopia, group 16SrIII was previously identified in NGS affected fields. However, no insect vectors or alternative hosts have been recorded for NGS in East Africa. During 2005, surveys were conducted at NGS-affected plantations of Debre-Zeit and Zwai field stations in Addis Ababa. Leaf samples were collected from weeds located in and surrounding the NGS-affected areas. Leafhopper species were also surveyed by vacuum sampling in a search for natural phytoplasma vectors. Total DNA was extracted from plants and insects, and used as a template in nested polymerase chain reaction (nPCR) with universal 16S rRNA phytoplasma primers. Restriction fragment length polymorphism (RFLP), sequencing of PCR products and phylogenetic analysis were conducted for a finer identification and characterization of the phytoplasma associated with NGS. A 16SrIII-A phytoplasma with 100% of identity in the 16S rRNA sequence with that of the previously identified one in Napier Grass (accession no. DQ305977 ) was identified from alfalfa, Medicago sativa (accession no. DQ305982 ), Cynodon dactylon (accession no. DQ3058983 ), Exitianus sp. ( DQ305980 ) and Leptodelphax dymas collected in Debre Zeit (accession no. DQ305979 ) and Zwai (accession no. DQ305978 ). These findings suggest that M. sativa and Cy. dactylon are alternative reservoirs, and Exitianus sp. and L. dymas , potential vectors of the 16SrIII-A phytoplasma, which may have epidemiological implications in spreading NGS in Ethiopia.