uv spectra were acquired 
 in spectroscopy grade meoh using an agilent 8453 uv  vis spectrophotometer ; 
 nmr spectra were recorded on bruker avance iii 600 mhz ( bruker biospin ) 
 and varian inova 500 mhz nmr spectrometers .
measured chemical shifts 
 were referenced to residual solvent ( h 2.50 and 
 c 39.5 in dmso - d6 ) . 

lcms analyses and hresims measurements were performed with an xterra 
 ms c18 ( 2.1  50 mm , 3.5 m , waters ) column 
 on a waters acquity uplc system coupled to a waters lct premier tof 
 mass spectrometer , a waters acquity pda detector , and a sedex 75 evaporative 
 light scattering detector .
preparative - scale purification 
 was performed with a dynamax 60  c18 column ( 19  
 300 mm , varian ) on an hplc system consisting of a waters 600 pump , 
 a waters 3100 mass detector , a waters 996 photodiode array detector , 
 and a shimadzu elsd - lt2 evaporative light scattering detector .
fusarium pallidoroseum ( atcc 74289 ) was maintained on difco potato dextrose agar at room 
 temperature .
saccharopolyspora erythraea ( atcc 31772 ) 
 was maintained on international streptomyces project medium 2 ( isp2 ) 
 agar , consisting of malt extract , 10 g / l ; dextrose , 4 g / l ; and yeast 
 extract , 4 g / l , at 27 c .
s. erythraea and f. pallidoroseum were grown on agar for two 
 weeks and one week , respectively , before inoculation into 100 ml of 
 isp2 seed medium in 500 ml erlenmeyer flasks .
both organisms were 
 incubated at room temperature for 24 h on a rotary shaker ( 150 rpm ) , 
 after which the seeds were used to inoculate 1 l erlenmeyer flasks 
 containing 200 ml of isp2 broth .
the inoculum per 1 l flask was 20 
 ml of s. erythraea and 1 ml of f. pallidoroseum with a ratio of packed cell volume to media of < 0.5 ml/15 ml 
 and 1 ml/15 ml , respectively .
fermentation was carried out for 4 days 
 at 27 c on a rotary shaker ( 200 rpm ) .
single control cultures 
 of s. erythraea and f. pallidoroseum were grown under identical conditions .
the full volume ( 3.5 
 l ) of culture filtrate was concentrated to 300 ml in vacuo ( < 40 c ) and partitioned three times with equal volumes 
 of ethyl acetate .
evaporation of the pooled organic layers yielded 
 1.45 g of an oily brown crude extract .
the extract was applied to 
 a 10 ml spe cartridge packed with 1.5 g of c18 silica . 

the cartridge was eluted in a stepwise fashion with increasing percentages 
 of meoh in h2o .
fractions containing the compounds of interest 
 were pooled and lyophilized , yielding 52.4 mg of enriched extract . 

further purification was performed with a stepwise gradient ( h2o / acn w/0.1% f.a . ;
020 min 65:35 , 2060 min 
 60:40 ; 6080 min 55:45 ; 10 ml / min ) on a preparative - scale reversed - phase 
 hplc system .
analysis and pooling of the resulting fractions afforded 
 ophiosetin ( 2.53 mg ) , n - demethylophiosetin ( 1 ) ( 2.86 mg ) , pallidorosetin a ( 2 ) ( 1.59 mg ) , 
 pallidorosetin b ( 3 ) ( 1.06 mg ) , and equisetin ( 5.07 mg ) .
[ ]d 334 ( c 0.025 , chcl3 ) ; cd ( c 0.1 mm , meoh ) max (  ) 232 ( 3.3 ) , 250 ( 2.3 ) , 
 285 ( 8.4 ) , 323 ( + 0.7 ) nm ; uv ( meoh ) max ( log 
  ) 250 ( 3.73 ) , 287 nm ( 3.92 ) ; h
nmr ( 500 mhz , dmso - d6 ) and c nmr ( 150 mhz , dmso - d6 ) see table 1 ; hresims m / z 376.2108 [ m + h ] ( calc 
 for c21h30no5 , 376.2124 ) .
[ ]d 153 ( c 0.025 , chcl3 ) ; cd ( c 0.1 mm , 
 meoh ) max (  ) 228 
 ( 4.0 ) , 256 ( 2.5 ) , 292 ( 11.5 ) , 324 ( + 2.5 ) nm ; 
 uv ( meoh ) max ( log  ) 251 ( 3.98 ) , 292 nm ( 3.99 ) ; h nmr ( 500 mhz , dmso - d6 ) and c nmr ( 150 mhz , dmso - d6 ) see 
 table 1 ; hresims m / z 390.2262 [ m + h ] ( calc for c22h32no5 , 390.2280 ) . [ ]d 142 ( c 0.025 , chcl3 ) ; cd ( c 0.1 mm , meoh ) max (  ) 237 
 ( 1.6 ) , 250 ( 1.6 ) , 293 ( 4.4 ) , 323 ( + 1.0 ) nm ; 
 uv ( meoh ) max ( log  ) 250 ( 3.76 ) , 290 nm ( 3.73 ) ; h nmr ( 500 mhz , dmso - d6 ) and c nmr ( 150 mhz , dmso - d6 ) see 
 table 1 ; hresims m / z 388.2115 [ m 
[ ]d 258 ( c 0.025 , chcl3 ) ; cd ( c 0.1 mm , 
 meoh ) max (  ) 234 ( 4.5 ) , 255 
 ( 1.7 ) , 292 ( 8.3 ) , 326 ( + 0.6 ) nm . [ ]d 241 ( c 0.025 , 
 chcl3 ) ; cd ( c 0.1 mm , meoh ) max (  ) 234 ( 4.2 ) , 256 ( 2.2 ) , 
 292 ( 7.7 ) , 328 ( + 0.3 ) nm .
 coculture of the fungus fusarium 
 pallidoroseum with 
 the bacterium saccharopolyspora erythraea was found 
 to produce three new 
 decalin - type tetramic acid analogues related to equisetin . 
 the structures 
 were determined by spectroscopic methods . 
 the absolute configurations 
 were established by circular dichroism spectroscopy and comparing 
 the data with those of equisetin . 
Experimental Section