Further lead optimization efforts on previously described 1, 2, 3, 4, 10, 10a-hexahydro-1H- pyrazino [1, 2-a] indoles led to the new class of 5, 5a, 6, 7, 8, 9-hexahydro-pyrido [3′, 2′: 4, 5] pyrrolo [1, 2-a] pyrazines culminating in the discovery of (5aR, 9R)-2- [(cyclopropylmethoxy) methyl]-5, 5a, 6, 7, 8, 9-hexahydro-9-methyl-pyrido [3′, 2′: 4, 5] pyrrolo [1, 2-a] pyrazine 18 as a potent, full 5-HT2C receptor agonist with an outstanding ...