Synthesis of 6 α , 7 β-Di-Hydroxyvouacapan-17 β-Oic Acid Derivatives Part III : Synthesis , 1 Hand 13 C-NMR of Amide Derivatives 1

Sete no vas ami das (III-IX) de ri va das do áci do 6α,7β-di-hidroxivouacapan-17β-ói co I (ADV) fo ram sin te ti za das. Suas es tru tu ras fo ram de ter mi na das atra vés da aná li se de da dos es pec tro mé tri cos, des ta can do-se os re sul ta dos for ne ci dos pe las ex pe riên ci as de RMN bi di men si o na is de cor re la ção de des lo ca men tos quí mi cos ho mo nu cle ar (H x H-COSY) e he te ro nu cle ar (H x C-COSY).


Intro duc ti on
The ge nus Pte ro don is wi dely dis tri bu ted in the Bra zi lian sa van nah, and in clu des dif fe rent spe ci es among which P. ap pa ri ci oi Pe der so li and P. poly ga la e flo rus Benth are com monly know as "Su cu pi ra-Branca" 2 .Alco ho lic in fu sions from the fru it are em plo yed in Bra zi li an folk me di ci ne for rhe u ma tic af fec ti on and thro at in fec ti ons 3 .Sin ce it was ve ri fi ed that the fu ra ne-diterpene 6 α,7 β-di-hydroxyvoua ca pan-17 β-oic acid I (ADV), iso la ted from the he xa ne extract from the fru it of Pte ro don poly ga la e flo rus Benth, presents an ti-inflammatory and anal ge sic ac ti vity 3,4 , a va ri ety of de ri va ti ves of ADV has been synthe si zed in or der to obta in more in for ma ti on about the struc tu re-activity re la tions hip of this se ri es of com pounds 4,5 .
Here we now re port the synthe sis of se ven new ami de de ri va ti ves of I, ac cor ding to Sche me 1, and the com ple te as sign ment of the ir 1 H-and 13 C-NMR data.The main purpo se of this pa per is the struc tu ral cha rac te ri za ti on of the se com pounds em plo ying ma inly one-and two-dimensional NMR.

Expe ri men tal
All re ac ti ons were fol lo wed by analy ti cal thin-layer chro ma to graphy (TLC, Merck Sí li ca Gel 60G, 3:2:1 he xane:dich lo ro met ha ne:et ha nol).Mel ting po ints were ob ser ved on a Met tler FP 82 HT and are not cor rec ted.Ele men tal analy ses were ob ta i ned on a Per kin Elmer 2400 ap pa ra tus.Infra red spec tra were ta ken on a Shi mad zu IR 408 spec tropho to me ter on KBr disks. 1 H-and 13 C-NMR spec tra were recor ded on a JEOL EX 400 ( 1 H: 400 MHz; 13 C: 100 MHz), Bru ker AC 200 ( 1 H: 200 MHz; 13 C: 50 MHz), or Bru ker AC 80 ( 1 H: 80 MHz; 13 C: 20 MHz) spec tro me ter.The NOE diffe ren ce spec trum was re cor ded on a Bru ker DRX 400 spec -Ar ti cle tro me ter.Te tra methylsi la ne was uti li zed as the in ter nal stan dard ( δ = 0).The 13 C sig nals due to CH/ CH 3 and CH 2 were as sig ned ac cor ding to the DEPT 135 13 C-NMR spectra.Mul ti pli ci ti es are in di ca ted by s (sin glet), d (dou blet),dd (dou ble dou blet), t (tri plet), q (quar tet), m (mul ti plet), and b (bro ad).Low re so lu ti on mass spec tra were ob ta i ned on a Vari an Mat 311 A ins tru ment ope ra ting at 70 eV.ADV de ri vati ves were pre pa red as in di ca ted in Sche me 1, ac cor ding to the met hods des cri bed be low 1 .

Re sults and Dis cus si on
A ge ne ral pre pa ra ti on pro ce du re for the ami de de ri va tives of ADV is des cri bed.The most ef fi ci ent synthe tic rou te for this pre pa ra ti on uti li zed 6 α-hydroxy vou a capan-7 β,17 β-lac to ne II (Sche me 1), sin ce the ope ning of the lac to ne group is en tro pi cally fa vo red.The lac to ne II was ob ta i ned by re ac ting ADV with ace tic anhydri de in the presen ce of anhydrous so di um ace ta te, in THF, as pre vi ously re por ted 4 .
The re ac ti ons were mo ni to red by TLC, the di sap pe aran ce of the IR band of the car bonyl lac to ne at ν 1770 cm -1 , and the ap pe a ran ce and in ten si fi ca ti on of bands I and II at 1680-1630 and 1570-1515 cm -1 , res pec ti vely, which are cha rac te ris tic of ami de groups 6 .
Some ad di ti o nal com ments may be made re gar ding the re ac ti vity of the ami nes em plo yed (Ta ble 1).The re la ti ve re ac ti vi ti es in the ca ses of propyl and iso propy la mi ne used for the pre pa ra ti on of VIII and IX , res pec ti vely, were in fluen ced by ste ric fac tors.In the synthe sis of VIII the re ac ti on time was ap pro xi ma tely 1/10 of that ne ces sary when isopropy la mi ne was em plo yed.The use of eth yle ne di a mi ne could sug gest a very fa vo ra ble re ac ti on due to the pre sen ce of two NH 2 groups.Ho we ver, the re ac ti on time and the low yi eld of VII re ve a led a low re ac ti vity of eth yle ne di a mi ne as com pa red to propy la mi ne.This re ac ti on dif fi culty may be due to the exis ten ce of in tra mo le cu lar hydro gen bon ding in eth yle ne di a mi ne.On the ot her hand, the ste ric ef fect should be the prin ci pal fac tor de ter mi ning the fa ci lity of the se reac ti ons, sin ce des pi te the ir hig her ba si city, di subs ti tu ted ami nes show a lo wer nu cle op hi lic abi lity due to ste ric hindran ce.This con si de ra ti on is sup por ted by the fact that the synthe sis of VI took lon ger than all the ot hers, as shown in Ta ble 1.
The struc tu res of all com pounds were de ter mi ned by spec tral pro per ti es (see the ex pe ri men tal part).The as signment of the 1 H and 13 C-NMR sig nals was ba sed on the obser ved sig nal mul ti pli ci ti es and em pi ri cal shift ru les, along with the 1 H x 13 C-COSY shift cor re la ti ons (Ta bles 2 and 3, res pec ti vely) 7,8 .
The as sign ments of the 1 H-NMR sig nals of the di terpe ne ske le ton atoms for all ami des shown in Ta ble 2 may be bet ter un ders to od by a more de ta i led analy sis of ami de IX , ta ken as a re fe ren ce, who se 1 H x 13 C COSY and 1 H x 1 H COSY spec tra are de pic ted in Figs. 1 and 2, res pec tively.
The hig her shi el ding re gi on ( δ 0.8-1.7) of the 1 H-NMR spec trum of the ADV de ri va ti ves is very com plex due to the over lap ping of the methyl, meth yle ne, and meth yne sig nals of the di ter pe ne mo i ety.The 1 H x 13 C-COSY Ta ble 2. 1 H che mi cal shifts ( δ) of the ami de de ri va ti ves of ADV * 1,2,3,5,9 0.8-2.00.8-1.170.9-1.180.8-1.80.9-1.65 0.  *Some cou pling cons tants J in Hz are in pa rent he ses.The che mi cal shifts and cou pling cons tants for com pounds III , V, VI and VII were de du ced from the 1D NMR spec tra. 1 H x 1 H-COSY and 1 H x 13 C-COSY were also used to con firm the che mi cal shift as sign ments, ma inly tho se of compounds IV , VIII , and IX .For as sign ments of the N-substituent hydro gen groups, see the Expe ri men tal part.** Cou pling cons tant va lu es in the Expe ri men tal part.# D 2O ex chan ge a ble.spec trum of IX (Fig. 1) con fir med the as sign ment for hydro gens at ta ched to C18, C19, and C20, ob ser ved at δ 1.17, 1.06 and 0.99, res pec ti vely.The axi al and equa to ri al hydro gens be lon ging to the meth yle ne at po si ti ons 1, 2, and 3 (H1, H2, and H3) sho wed re sol ved sig nals in the 1 H x 13 C-COSY spec trum (Fig. 1).The mul ti pli ci ti es, che mi cal shifts, and cou pling cons tant va lu es for the H11 meth yle ne were used for the ste re o che mistry as sign ment of both H11ax and H11eq.The mul ti plet in the δ 2.3-2.4 ran ge was as sig ned to hydro gen at the axi al po si ti on (J gem = 16.0Hz, J11ax-9 = 11.5 Hz).The lat ter va lue con firms the axi al-axial re la ti ons hip bet we en H9 and H11ax.Be si des the se two cou pling cons tant va lu es, anot her of 2.2 Hz was ob ser ved, cor res pon ding to the long ran ge cou pling 5 J bet we en H11ax and H14.The 1 H x 1 H-COSY spec trum con fir med this as sign ment (Fig. 2).The hydro gen H11 in the equa to rial po si ti on sho wed a dou ble dou blet at δ 2.68 (J gem = 16.0Hz, J 11eq-9 = 5.0Hz).The lat ter va lue con firms the axial-equatorial ste re o che mistry bet we en hydro gen H9 and H11.
For all ami des ( III to IX) the 1 H-NMR spec tral data due to the N-alkyl subs ti tu ent are pre sen ted in the Expe ri men tal part.In the case of ami de IX , two dou blets of equal in tensity at δ 1.14 and δ 1.15 cha rac te ri ze the methyl hydro gens of the iso propyl group.A mul ti plet bet we en δ 4.04 and 4.14, is also ob ser ved which is due to the cou pling of the iso propyl group meth yne hydro gen (H1' in Sche me 1) with both NH and the CH 3 groups (H2' and H2" in Sche me 1).The 1 H x 13 C-COSY spec trum sho wed cross cou pling betwe en H1'and the NH hydro gen at δ 5.62 (see Fig. 2).This mul ti plet was sim pli fi ed af ter the ad di ti on of D 2O, and showed two over lap ping hep tets, with an in ten sity ra tio of 3:1.This fact may in di ca te the con fi gu ra ti o nal iso me rism existing in ami des (E and Z iso mers), as il lus tra ted in Fig. 3.
Accor ding to the ste re o che mi cal analy sis of IX with Dri e ding mo dels, the en vi ron ment of the iso propyl group va ri es from iso mers E to Z both con fi gu ra ti o nally and confor ma ti o nally, be ing much less crow ded in the Z iso mer.On the ot her hand, con for mers Z 1 and Z 2 , pre sen ted in Fig. 3, could form hydro gen bonds bet we en eit her HO-HN δ + or OH--δO-C.Ho we ver, the se hydro gen bonds do not oc cur be ca u se the che mi cal shift for the OH7 group in CDCl 3 is at δ 2.0 or δ 4.0-4.2(Ta ble 2).If hydro gen bonds were pre sent, the hydro gen of the OH7 group would be much more des hiel ded 9 .Mo re o ver, be ca u se of the slo wer in ter mo le cu lar pro ton ex chan ge in DMSO-d 6 , the spec trum of IX in this sol vent shows du plets at δ 4.04 (J H7-OH = 4.3Hz) and δ 4.13 Ta ble 3. 13 C che mi cal shifts ( δ) of the ami de de ri va ti ves of ADV.(J H6-OH = 4.0 Hz) for OH7 and OH6, res pec ti vely.The se che mi cal shifts are also cha rac te ris tic of OH groups without hydro gen bon ding 6,9 .The re fo re, the two hep tets obser ved for the iso propyl meth yne hydro gen in the 1 H-NMR spec trum of IX may in di ca te eit her an equi li bri um bet we en E and Z iso mers or bet we en Z 1 and Z 2 con for mers.Furt her in for ma ti on about the se ste re o i so mers was deri ved from the NOE dif fe ren ce spec trum with the de coupling of NH hydro gen.

Car bon
NOE enhan ce ment ob ser ved for H14 (Ta ble 4) re flects a syn re la ti ons hip bet we en this hydro gen and the NH, in dica ting the pre sen ce of the Z con for mer.The hig her NOE va lue for H14 (7.0), as com pa red to that for H15 (3.5), shows a Z 1 pre pon de ran ce over Z 2 .The weak NOE ef fect ob ser ved for H8 and OH7 shows some spa ti al pro xi mity of NH.This pro xi mity is pos si ble only in the Z 1 form.
The 13 C-NMR (DEPT 90, 135, BB de cou pled spectrum, and 1 H x 13 C-COSY spec tra) con fir med the as signments for the car bon atoms of the iso propyl group.Its methyl groups are mag ne ti cally no ne qui va lent due to the chi ral ne igh bor ho od, in de pen dent of the con for ma ti o nal pro blem dis cus sed abo ve.
The re ac ti on of the fu ra ne-diterpene lac to ne II with a wide va ri ety of ami nes was shown to be a con ve ni ent and ver sa ti le met hod for ami de de ri va ti ves pre pa ra ti on.The struc tu ral cha rac te ri za ti on of the se com pounds em plo ying one and two-dimensional 1 H and 13 C-NMR may be qui te in te res ting for re se ar chers, in the fi elds of na tu ral pro ducts and synthe tic che mistry.

Fi gu re 2 .Fi gu re 1 .Fi gu re 3 .
The 1 H x 1 H 2D shift cor re la ted spec trum of IX .The 1 H x 13 C 2D shift cor re la ted spec trum of IX .Con fi gu ra ti on iso mers (E/Z) and con for mers (Z1/Z2) pos si ble for IX .

Sche me 1. Synthe sis of ami de de ri va ti ves III to IX . Ta ble 1. Sum
mary of the data for the pre pa ra ti on of the ami de de ri va ti ves of ADV.