It is increasingly clear the need to fill spaces at the interface between science and decision-making. However, there is still a lack of institutional initiatives acting on these interfaces. We argue here that initiatives based on synthesis science can help bridge this gap if they are based on a transdisciplinary and participatory approach. These initiatives or institutions can function as boundary organizations, intermediating the relations between the demands of decision-makers and society, and the different processes of knowledge generation. Understanding the potential of these initiatives may help identify gaps and opportunities for strengthening and improving actions on science and decision-making interface, including capacity building in megadiverse countries. Brazil has been advancing in structuring synthesis initiatives with this perspective of exploring the science-conservation interface. The main objective of this presentation will be to share the lessons learned from two of these initiatives: the Synthesis Center on Biodiversity and Ecosystem Services (SinBiose), implemented as a research program at the Brazilian National Council for Scientific Research (CNPq), and the Biota Synthesis project, a state initiative focused on supporting the state of São Paulo in the development of socio-environmental public policies, considering essentially nature-based solutions. Although recent, these two initiatives show the great potential of synthesis initiatives in filling the implementation gap of socio-environmental public policies in megadiverse countries.