Coumarinolignans from the Seeds of Annona squamosa Linn

Phytochemical investigations of Annona squamosa seeds have led to the isolation of three lignans consisting of coumarin moiety, cleomiscosin A(1), cleomiscosin B(2) and cleomiscosin C(3). Their structures were arrived at by detailed spectroscopic analysis. Cleomiscosin A and cleomiscosin B are position isomer.


Introduction
A. squamosa Linn. is commonly known as the custard apple.It is native of West Indies and has been naturalized throughout India in plains as well as on hills 1,2 .A. squamosa L. is a well known edible tropical fruit and its seeds exhibit insecticidal and abortifacient properties 3 .A. Squamosa consists of a variety of compounds e.g.amino acids 4 monoterpenes 5 , sesquiterpenes 6 , kaurene 7 , steroids 8 etc.Our previous studies have resulted in the isolation of about 30 acetogenins from the seeds of A. squamosa, eg.Squamostanal-A 9 , Squamosin-O 1 and O 2 10 , squamosatin-A, Squamocins B-to-N 11 etc.In continuation of our work we report herein isolation and identification of compounds 1-3 from seeds of Annona squamosa.
Table 1. 1 H-(500 MHz) and 13 C-NMR (125) data for 1 and 2 (in DMSO-d 6 ) and 3 (in CDCl 3 ).Melting points were determined by using the Yazawa hot stage apparatus and are uncorrected.Optical rotations were recorded JASCO DIP-360 Polarimeter (cell length 5 cm).UV was recorded on JASCO UV / visible spectrophotometer (model no.7800).IR on JASCO FT-IR 5300 Spectrophotometer.NMR spectra were recorded on Bruker DRX 500 or JEOL GSX 500 with TMS as an internal refrence.SiO 2 gel (Qualigens 60-120 mesh) was used for column chromatography and TLC was performed on pre-coated Silica gel G (Merck).All solvents were distilled prior to their use.

Compound 1
1 H-NMR spectrum showed the presence of two doublets at δ H 6.33 and 7.95 (1H, d, J= 9.5 Hz) for olefinic hydrogens and one aromatic proton signals at δ H 6.90 (1H, s) is suggesting the presence of 6,7,8 trioxygenated coumarin moiety in the compound 1. the spectrum also showed aromatic signals at δ H 7.06, 6.89 and 6.82 for 1,3,4 tri-substituted aromatic nucleus, these three aromatic hydrogens taken along with the up-field hydrogen signals at δ

Compound 2
The spectroscopic data of compound 2 were virtually identical with cleomiscosin A, but it differs from it in their physical properties like R t on HPLC, the R f value and the melting point.These allowed us to infer that compound 2 may be a regioisomer of cleomiscosin A i.e.Cleoiscosin B. Indeed it was found so when compared with an authentic sample of cleomiscosin B in respect to their R t , R f value and melting point.

Compound 3
It is a minor congener of cleomiscosins A and B. The 1 H-NMR spectrum of compound 3 showed signals for all the hydrogens as exhibited in compounds 1 and 2. The main difference was observed by the presence of one additional methoxy signal at δ H 3.97 (3H, s) at the cost of one proton of ABX system present in the lignan part of the molecule.A comparison of the 1 H-NMR data of compound 3 with the relevant data of other reported coumarinolignans it was found to match well with cleomiscosin C. It showed identical R t , R f value and melting point when compared with an authentic sample of cleomscosin C.