This paper presents a complete design methodology, from behavioral modelling to lab prototyping and validation, of a Distributed Unit (DU) lower physical layer transmission chain, for Fifth Generation (5G) New Radio (NR) wireless communication technology. The case study presented follows a model-driven engineering and prototyping approach, starting with a high-level behavioral model, which is refined and validated in a iterative way, until an hardware implementation is obtained and validated. Fast prototyping is achieved through the adequate combination of languages (Matlab, Simulink and VHDL), simulation and FPGA-based synthesis and debug tools. Simulation-based validation is performed at different stages of the design flow, from behavioral descriptions using floating-point precision, to cycle-accurate models using fixed-point representations. The DU transmission chain supports currently the Frequency Range 1 (FR1) of 5G-NR with a configurable channel bandwidth up to 100 MHz. However, the implemented solution is flexible and modular supporting the configuration of different communication parameters and interfaces for next generation networks. This is achieved through the parametrization of the models and implementation into MPSoC devices to be connected to Software Defined Radio RF frontends, using an automated design flow. Since the complete design occupies less than 5% of the MPSoC resources, the integration of the uplink reception chain and the creation of multiple instances for communication diversity can be done.