I, N., H. S, H. A. Hadi, and K. Awang. “Ab Initia Geometry-Optimization and NMR Studies of Chemical Constituents of Piper Sarmentosum”. Malaysian Journal of Science, vol. 21, no. 1&2, Apr. 2002, pp. 143-7, http://mjs.um.edu.my/index.php/MJS/article/view/8600.