Hits to draw Markush structures:
1. Draw a R atom
2. Right click on the atom and choose "Create R Definition" menu item. It will create "R1=" label there.
3. Right click on the "R1=" label, and select "Add Structure" menu item, and it will create a substructure
4. You can edit the substructure
5. To change R index number, mouse-hover R atom, and press +/-.