You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
optical rotations were 
 measured on a jasco p-2000 polarimeter ( c g/100 ml ) 
 equipped with a halogen lamp ( 589 nm ) and a 1 ml microcell .
all nmr spectra were acquired with a varian mercuryplus 400 spectrometer 
 using solvent signals ( dmso - d6 : h , h 2.50 ; c , c 39.52 ; 
 cdcl3 : h , h 7.24 ppm ; c , c 77.23 ppm ) as references .
c correlations were determined 
 with gradient - enhanced inverse - detected hsqc and hmbc experiments , 
 respectively .
hplc was performed on a shimadzu 
 lc-20at instrument with a shimadzu spd - m20a uv / vis photodiode detector 
 and a shimadzu elsd - ltii detector .
the leaves of cornus florida l. were collected from 
 a one - mile radius around timber lake , oxford , 
 mississippi , during the spring and summer of 2011 by m.t.h .
voucher 
 specimens are kept in the hamann laboratory at the university of mississippi , 
 school of pharmacy , oxford , ms ( cf2011 ) .
the leaves of c. florida ( 15.0 
 kg , dry weight ) were extracted with 90% 
 aqueous ethanol and dried under reduced pressure to give a crude extract 
 ( 900 g ) .
a portion of this crude extract ( 400 g ) was separated on 
 a silica gel column ( 20  70 cm ) using a stepwise gradient of 
 hexanes / etoac ( 100:0 , 80:20 , 50:50 , and 0:100 , v / v , each 3 l ) and 
 etoac / meoh mixtures ( 80:20 , 60:40 , 50:50 , and 0:100 , v / v , each 3 l ) 
 to afford eight fractions .
fraction e ( 220 g ) was then chromatographed 
 on hp-20 ( 8  50 cm ) using a stepwise gradient of acetone / water 
 ( 10:90 , 20:80 , 50:50 , 60:40 , 80:20 , and 100:0 , v / v , each 2 l ) to give 
 six subfractions ( fr .
fraction 
 e2 ( 40 g ) was chromatographed on a preparative c18 reversed - phase mplc column ( 20  250 mm ; 2035% ch3oh / h2o over 40 min , 3565% ch3oh / h2o over 20 min ; flow rate : 12 ml / min ) to afford eight 
 subfractions ( fr . e2a 
e2h ) . fraction 
 e2d ( 4.0 g ) was chromatographed on a preparative c18 reversed - phase hplc column ( shim - pak rp - c18 column ; 
 5 m ; 20  250 mm ; 845% ch3cn / h2o over 120 min , 7 ml / min ) to yield eight subfractions ( fr . 
 e2d-1e2d-8 ) .
fraction 
 e2d-4 ( 50 mg ) was purified by c8 reversed - phase 
 hplc ( polar - c8 ; 5 m ; 10  250 mm ; 1545% 
 ch3oh / h2o over 90 min , 5 ml / min ) to yield cornusoside 
 a ( 1 , 5.0 mg , tr 76.2 min ) . 

fraction e2d-6 ( 832 mg ) was subjected to silica 
 gel column chromatography using ch2cl2/meoh 
 ( 90:10 to 0:100 , v / v ) to afford nine fractions ( fr .
fraction e2d-6-a ( 320 mg ) was further purified by c8 reversed - phase hplc 
 ( polar - c8 ; 5 m ; 10  250 mm ; 525% ch3cn / h2o over 70 min , 5 ml / min ) to yield two fractions . 
 the first fraction ( 60 mg )
was purified on a polymeric hplc column 
 ( hamilton prp-1 ; 5 m ; 20  250 mm ; 1040% ch3cn / h2o over 50 min , 7 ml / min ) to yield cornolactone 
 c ( 4 , 8.0 mg , tr 41.5 min ) . 

the second fraction ( 40 mg ) was chromatographed on a polymeric hplc 
 column ( hamilton prp-1 ; 5 m ; 20  250 mm ; 1545% 
 ch3cn / h2o over 70 min , 7 ml / min ) to yield cornolactone 
 b ( 3 , 4.0 mg , tr 37.9 min ) . 

cornolactones a ( 2 , 15.0 mg ) and d ( 5 , 12 
 mg ) were purified from the remaining crude extract ( 500 g ) using a 
 similar procedure ( see supporting information ) . colorless gum ; [ ]d 13.8 ( c 0.01 , meoh ) ; 
 uv ( meoh ) max ( log  ) 230 ( 3.4 ) nm ; ir ( kbr ) 
 max 3355 , 2922 , 1730 , 1073 , 1020 cm ; h and c nmr ( 400 mhz , d6-dmso ) , see table 1 ; hresims m / z 413.1417 [ m + na ] ( calcd 
 for c17h26o10na , 413.1418 ) . colorless gum ; [ ]d + 3.3 ( c 0.2 , meoh ) ; uv ( meoh ) 
 max ( log  ) 237 ( 3.2 ) nm ; ir ( kbr ) max 3355 , 2922 , 1730 , 1073 , 1020 cm ; h and c nmr ( 400 mhz , cdcl3 ) , see 
 table 1 ; hresims m / z 171.1010 [ m + h ] ( calcd for c9h15o3 , 171.1016 ) . colorless gum ; [ ]d 7.5 
 ( c 0.02 , meoh ) ; 
 uv ( meoh ) max nm 243 ( 3.1 ) nm ; ir ( kbr ) max 2944 , 1658 , 1023 cm ; h 
 and c nmr ( 400 mhz , cdcl3 ) , see table 2 ; hresims m / z 197.0811 
 [ m + h ] ( calcd for c10h13o4 , 197.0808 ) . colorless gum ; [ ]d + 13.3 ( c 0.03 , meoh )
; uv ( meoh ) 
 max ( log  ) 241 ( 3.1 ) nm ; ir ( kbr ) max 3337 , 2952 , 2937 , 1733 , 1650 , 1017 cm ; h and c nmr ( 400 mhz , cdcl3 ) , see table 2 ; hresims m / z 215.0884 [ m + na ] ( calcd for c11h16o5na , 215.0890 ) .
colorless gum ; [ ]d + 18.5 ( c 0.02 , meoh ) ; uv ( meoh ) 
 max ( log  ) 244 ( 2.8 ) nm ; ir ( kbr ) max 3401 , 2952 , 1733 , 1089 , 1068 cm ; h and c nmr ( 400 mhz , cdcl3 ) , see 
 table 2 ; hresims m / z 193.0834 [ m + na ] ( calcd for c9h14o3na , 193.0835 ) .
cornusoside a ( 1 ) ( 2 mg ) 
 was hydrolyzed by using 1 m hcl ( 0.4 ml ) at 100 
 c for 2 h under argon and neutralized with amberlite ir400 . 
 after drying under reduced pressure ,
the residue was dissolved in 
 pyridine ( 0.4 ml ) containing l - cysteine ethyl ester hydrochloride 
 ( 2 mg ) and heated at 60 c for 1 h. a 0.4 ml solution of 3,5-dichlorophenyl 
 isothiocyanate ( 2 mg ) in pyridine was added to the mixture , which 
 was heated at 60 c for 1 h. the reaction mixture was directly 
 analyzed by analytical hplc on a shim - pak rp - c18 column , 
 5 m , 4.6  250 mm , by eluting with a gradient of 3080% 
 ch3cn in h2o with 0.02% hcooh for 40 min and 
 subsequent washing of the column with 100% ch3cn at a flow 
 rate 0.8 ml / min . in the acid hydrolysate of 1 , d - glucose was confirmed by comparison of the retention times of their 
 derivatives with those of l - glucose and d - glucose 
 derivatives prepared in the same way , which showed retention times 
 of 34.8 and 34.0 min , respectively .
a new iridoid glucoside , cornusoside 
 a ( 1 ) , and four 
 new natural product iridoid aglycones , cornolactones a  d ( 25 ) , together with 10 known compounds 
 were isolated from the leaves of cornus florida . 
 
 the structures of compounds 15 were 
 established by interpretation of their spectroscopic data . 
 cornolactone 
 b ( 3 ) is the first natural cis - fused 
 tricyclic dilactone iridoid containing both a five- and a six - membered 
 lactone ring . 
 a biosynthesis pathway is proposed for cornolactones 
 c ( 4 ) and d ( 5 ) , the c-6 epimers of compounds 13 .