s = "John Smith<john.smith@somewhere.com>, Jane Smith<jane.smith@somewhere.com>"
a = s.scan(/<.+?@.+?>/).map{|e| e[1...-1]}

# you can optionally print the addresses on new lines

a.each {|e| print e; puts ","}

# this prints
#  john.smith@somewhere.com,
#  jane.smith@somewhere.com,