Conselho Nacional de Desenvolvimento Científico e Tecnológico / The present work describes the phytochemistry study and antimicrobial activity of the aerial parts and bark root of three species from Rhamnaceae family: Discaria americana Gilles & Hook, Colletia paradoxa Sprengel and Gouania ulmifolia Hook & Arnott. Four new cyclopeptide natural, discarene C (154), discarene D (155), discarine M (156), discarine N (157) and nine cyclopeptide alkaloids, adoutine Y (92), adoutine Y' (47), franganine (66), frangulanine (67), discarine A (59), discarine B (58), discarine C (100), discarine D (101) and myrianthine A (105), a pentacyclic triterpenoid, acid betulinic (192) and three sterols, β-Sitosterol (195), β-sitosterol-3-O-6-β-D-glucopyranoside (196) and β-sitosterol-3-O-6-stearoyl-β-D-glucopyranoside (197), were isolated of the bark root of D. americana, along with three compounds already described 192, 195, 196, two pentacyclic triterpenoids, ursolic acid (194) and ceanotic acid (193) and an ester derived from ferulic acid (198) of the aerial parts. From the aerial parts of C. paradoxa it was isolated a new compound, called seco-3,4-germanicone (205), along with the known compounds ursolic acid (194), lupeol (199), betulinic acid (192), ceanothic acid (193), taraxerol (200), taraxerone (201), seco-3,4-taraxerone (202), germanicol (203), germanicone (204), β-sitosterol (195) and β-sitosterol-3-O-6-β-D-glucopyranoside (196). From the bark root it was isolated zizyberenalic acid (206), along with compounds 192, 193, 194, 195 and 196. The extracts of the aerial parts of Gouania ulmifolia, two new pentacyclic triterpenoids were isolated, 2-hydroxy-2-nor-20(29)-lupen-27,28-dioic acid (208)and 24-hydroxy-A(1)-nor-2,20(29)-lupadien-27,28-dioic acid (209), along with the known compounds lupeol (199), betulinic acid (192), alphitolic acid (207), β-sitosterol (195) and β-sitosterol-3-O-6-β-D-glucopyranoside (196). All compounds are being described for the first time in the species. Additionally, antimicrobial activity of extracts, fractions and isolated compounds of Discaria americana, Colletia paradoxa and Gouania ulmifolia was analyzed, through the bioautography technique, measuring the inhibitory activity of the growth on different microorganisms, three Gram positive bacteria (Staphylococcus aureus, Bacillus subtilis, Staphylococcus epidermidis) and four Gram negative bacteria (Klebsiella pneumonia, Salmonella setubal, Escherichia coli and Pseudomona aeruginosa) and the fungus (Saccharomyces cerevisiae and Candida albicans). / O presente trabalho descreve o estudo fitoquímico e antimicrobiano das partes aéreas e casca da raiz de três espécies pertencentes à família Rhamnaceae: Discaria americana Gilles & Hook, Colletia paradoxa Sprengel e Gouania ulmifolia Hook & Arnott. Quatro novos ciclopeptídeos naturais, discareno C (154), discareno D (155), discarina M (156), discarina N (157) e nove alcalóides ciclopeptídicos, adoutina Y (92), adoutina Y (47), franganina (66), frangulanina (67), discarina A (59), discarina B (58), discarina C (100), discarina D (101) e miriantina A (105), um triterpeno pentacíclico, ácido betulínico (192) e três esteróides, β-sitosterol (195), β-sitosterol glicosilado (196) e β-sitosterol 6'-O-acil glicosilado (197), foram isolados da casca da raiz de D. americana, juntamente com três compostos já descritos 192, 195, 196, dois triterpenos pentacíclicos, ácido ursólico (194) e ácido ceanótico (193) e um éster derivado ácido ferúlico (198) das partes aéreas. Das partes aéreas de C. paradoxa isolou-se um novo metabólito, denominado seco-3,4-germanicona (205), juntamente com os compostos conhecidos, ácido ursólico (194), lupeol (199), ácido betulínico (192), ácido ceanótico (193), taraxerol (200), taraxerona (201), seco-3,4-taraxerona (202), germanicol (203), germanicona (204), β-sitosterol (195) e β-sitosterol glicosilado (196). Da casca da raiz foi isolado ácido ziziberenálico (206), juntamente com os compostos 192, 193, 194, 195 e 196. Dos extratos das partes aéreas de Gouania ulmifolia foram isolados dois novos triterpenos pentacíclicos, ácido 2-hidroxi-2-nor-20(29)-lupen-27,28-dióico (208) e ácido 24-hidroxi-A(1)-nor-2,20(29)-lupadien-27,28-dióico (209), juntamente com os compostos conhecidos lupeol (199), ácido betulínico (192), ácido alfitólico (207), β-sitosterol (195) e β-sitosterol glicosilado (196). Todos compostos estão sendo descritos pela primeira vez na espécie. Adicionalmente, foram analisadas as atividades antimicrobianas dos extratos, frações e metabólitos isolados de Discaria americana, Colletia paradoxa e Gouania ulmifolia, através da técnica de bioautografia, medindo-se as atividades inibitórias do crescimento sobre diferentes microorganismos, três bactérias Gram positivas (Staphylococcus aureus, Bacillus subtilis, Staphylococcus epidermidis) e quatro bactérias Gram negativas (Klebsiella pneumonia, Salmonella setubal, Escherichia coli e Pseudomona aeruginosa) e os fungos (Saccharomyces cerevisiae e Candida albicans).