ISOLATION AND IDENTIFICATION OF DITERPENES FROM ALISMA ORIENTALIS JUZEP

AIMTo investigate the chemical constituents of the rhizomes of Alisma orientalis Juzep. METHODSThe compounds were isolated with silica gel chromatography and their planar structures were elucidated on the basis of chemical evidences and spectral analyses (IR, EIMS, ESIMS, ¹HNMR, ¹³CNMR, INEPT, ¹H-¹H COSY, HMQC, HMBC). The structure of I was determined to be kaurane-2, 12-dione by x-ray experiment previously, but the chemical shifts of I were not assigned. The 13CNMR of oriediterpenol (II) was similar to that of I except C-2, C-3. The chemical shifts of I were assigned by 2D-NMR (¹H-¹H COSY, HMQC, HMBC). The ¹H-¹H COSY and TOCSY spectrum did not show correlation between 13-H and 16-H, so the dihedral angle between 13-H and 16-H was supposed to be nearly vertical and the infer was confirmed by molecule modeling. The NOESY spectrum and biogenetic paths showed that the relative stereostructure of oriediterpenol (II) is the same as I. The absolute stereostructure can be established by CD studies and molecule modeling methods. The chemcal shift of 3-H (δ 3.19) and the coupling constant J_2a,3=12 Hz and J_2e,3=5 Hz revealed that the 3-hydroxy is equatorial hydroxy. The configuration type of II was determined to be a ent-kaurane diterpene by molecule modeling and CD spectrum using octant rule, the evidence indicated that the absolute configuration at 16-position in oriediterpenol (II) to be R. Aglycone and sugar part was obtainted after hydrolysis of oriediterpenoside (III). The aglycone of oriediterpenoside (III) was identical with oriediterpenol (II) (IR and NMR data). The sugar part of oriediterpenoside (III) was determined to be D-xylose comparing with standard compound (TLC). The linkage between aglycone and sugar was determined by 2D-NMR (TOCSY, HMBC and NOESY). In the HMBC spectrum the correlation from the anomeric 1′-H to C-3 indicated that D-xylose was connected to C-3. The β configuration of the glucoside bond was deduced by the coupling constant J_1′,2′ of 7.5 Hz. RESULTSThree ent-kaurane diterpenes were isolated from the rhizomes of Alisma orientalis Juzep. They were elucidated as 16(R)-ent-kaurane-2,12-dione (I), 16(R)-3-hydroxy-ent-kaurane-12-one (II), 16(R)-ent-kaurane-12-one 3α-O-β-D-xyloside (III). CONCLUSIONCompound II and III are new ent-kaurane diterpenes and were named as oriediterpenol and oriediterpenoside.