Install error - Could not build against OpenSSL but have OpenSSL installed

[God Atum]

Dear all,

I have OpenSSL installed, package openssl-1.0.1e-4.53.amzn1.x86_64

I have downloaded Openconnect v5.01. When I run "sudo ./configure" I
get the error:

checking for GNUTLS... no
checking for OPENSSL... no
checking for OpenSSL without pkg-config... no
configure: error: Could not build against OpenSSL

Any help will be greatly appreciated.

Many thanks,
Chris