So it looks like the PREROUTING chain does not exist in the filter table. When attempting to drop packets in the PREROUTING chain, you need to specify the table. For instance, the nat table:

iptables -t nat -A PREROUTING -p tcp -i eth2 -s 10.18.83.0/24 -d ! 172.16.0.0/12 -m multiport –dports 80,8080 -j DNAT –to 172.19.100.206:80