An Asymmetric Synthetic Approach to the A-ring of the Taxol Family of Anti-Cancer Compounds*
A synthetic route developed for the preparation of the A-ring of Taxol family of molecules is reported. By means of an intramolecular Diels-Alder reaction an asymmetric approach to this ring has been accomplished. Also, initial studies to prepare the A ring using an intramolecular Diels-Alder reaction have been successful.
Stereocontrolled synthesis of N,O-dimethyl-γ-amino-β-hydroxy acids : analogues of the (R)-MeIle-ψ(CHOMe)-Gly residue of the cytotoxic marine pseudopeptide dolastatin 10☆
Abstract The stereocontrolled synthesis of the N,O-dimethylated-γ-amino-β-hydroxy acid (R)-MeVal-ψ(CHOMe)-Gly ( 3b ) is reported; the key step is the formation of the nonmethylated allylic precursor with the anti configuration 20 by reduction of the keto analogue 16 .
Remote estimation of nitrogen and chlorophyll contents in maize at leaf and canopy levels
a b s t r a c t Leaf and canopy nitrogen (N) status relates strongly to leaf and canopy chlorophyll (Chl) content. Remote sensing is a tool that has the potential to assess N content at leaf, plant, field, regional and global scales. In this study, remote sensing techniques were applied to estimate N and Chl contents of irrigated maize (Zea mays L.) fertilized at five N rates. Leaf N and Chl contents were determined using the red-edge chlorophyll index with R2 of 0.74 and 0.94, respectively. Results showed that at the canopy level, Chl and N contents can be accurately retrieved using green and red-edge Chl indices using near infrared (780-800 nm) and either green (540-560 nm) or red-edge (730-750 nm) spectral bands. Spectral bands that were found optimal for Chl and N estimations coincide well with the red-edge band of the MSI sensor onboard the near future Sentinel-2 satellite. The coefficient of determination for the relationships between the red-edge chlorophyll index, simulated in Sentinel-2 bands, and Chl and N content was 0.90 and 0.87, respectively.