Cyclooctyne [60]fullerene hexakis adducts: a globular scaffold for copper-free click chemistry

Jou nal Name COMMUNICATION This jou nal is © The Royal Socie y o Chemis y 20xx J. Name., 2013, 00, 1-3 | 1 Please do no adjus ma gins Please do no adjus ma gins a. Depa amen o de Química O gánica, Fac. CC. Químicas, Uni e sidad Complu ense de Mad id, A . Complu ense s/n, 28040 Mad id (Spain). b. Glycosys ems Labo a o y, Ins i u o de In es igaciones Químicas (IIQ), CSIC- Uni e sidad de Se illa, A . Amé ico Vespucio 49, 41092 Se ille (Spain). c. IMDEA-Nanoscience, Campus Can oblanco, 28049 Mad id (Spain). d. These au ho s con ibu ed equally o his wo k. † Foo no es ela ing o he i le and/o au ho s should appea he e. Elec onic Supplemen a y In o ma ion (ESI) a ailable: [de ails o any supplemen a y in o ma ion a ailable should be included he e]. See DOI: 10.1039/x0xx00000x Recei ed 00 h Janua y 20xx, Accep ed 00 h Janua y 20xx DOI: 10.1039/x0xx00000x www. sc.o g/ Cyclooc yne [60]Fulle ene Hexakis Adduc s: a Globula Sca old o Coppe -F ee Click Chemis y Ja ie Ramos-So iano,a,b,d José J. Reina,b,d Al onso Pé ez-Sánchez,a Bea iz M. Illescas,*a Ja ie Rojo*b and Naza io Ma ín*a,c The syn hesis o a new highly symme ic hexakis adduc o C60 appended wi h 12 cyclooc yne moie ies has been ca ied ou . This compound has been used o he coppe - ee s ain-p omo ed cycloaddi ion eac ion o a se ies o azides wi h excellen yields. This s a egy o he ob en ion o clicked adduc s o [60] ulle ene is o special in e es o biological applica ions. [60]Fulle ene hexakis adduc s wi h Th symme y cons i u e an a ac i e class o compounds ha allow he globula disposi ion o subs i uen s a ound he C60 co e.1 These compounds ha e a ac ed much a en ion in he las ecen yea s, bo h in he a eas o ma e ials science and biomedicine. Thus, some o hem p esen liquid c ys al beha io ,2 ha e been employed o he s udy o elec onic and ene gy ans e p ocesses,3 as o ganic connec i i y cen e s o he syn hesis o Me al O ganic F amewo ks (MOFs),4 o as ca alys s.5 On he o he hand, in he a ea o biological applica ions, hei ac i i y has been es ed in di e en ields showing in e es ing p ope ies and good biocompa ibili y. Hexakis adduc s o [60] ulle ene ha e been es ed as gene ans ec ion ec o s,6 mul iplying uni s o pho odynamic he apy,7 glycosidase and glycosyl ans e ase inhibi o s,8 o e icien an ibac e ial9 o an i i al sys ems.10 The syn hesis o hese adduc s was i s s udied by Hi sch by he one-po addi ion o malona es empla ed by 9,10- dime hylan h acene11 and la e modi ied by Sun.12 Howe e , hese p ocedu es a e o en limi ed by he size o he malona es, as he s e ic aspec s limi he yield o he eac ion. To o e come his d awback, Nie enga en p oposed he employmen o an azide appended malona e o ob ain a clickable hexakis adduc o C60 o e ec i ely allow he co alen unc ionaliza ion o [60] ulle ene by Cu(I) alkyne-azide cycloaddi ion (CuAAC) eac ion.13 La ely, Nie enga en and we desc ibed he 12-alkyne modi ied hexakis adduc o [60] ulle ene and i s use in he click chemis y addi ion o azides and alkynes.14 This e ec i e eac ion equi es, howe e , he use o coppe (I) as ca alys , which in ol es a subsequen pu i ica ion s ep o he emo al o coppe , especially wi h hose ma e ials o bio-medical applica ions, owing o i s high cy o oxici y. This s ep can be hampe ed by he p esence in he inal p oduc s o unc ional g oups, and e en he iazole ings hemsel es, capable o binding coppe , hus limi ing hei biological applica ions.15 A s a egy o a oid his pu i ica ion s ep is o employ o s ain p omo ed alkyne-azide cycloaddi ion (SPAAC) click eac ion. This eac ion, de eloped by Be ozzi and cowo ke s,16 consis s o he eac ion o s ained cyclooc ynes wi h azides and has ecei ed conside able a en ion owing o i s simplici y and as e eac ion a es, a oiding he use o a me al as ca alys . As i does no equi e he use o coppe , i has especial ele ance o biological applica ions. In he p esen communica ion we epo he syn hesis o a new hexakis adduc o [60] ulle ene subs i u ed wi h wel e cyclooc yne moie ies o u he ca y ou SPAAC eac ions. The e sa ili y o his new de i a i e has been es ed wi h he addi ion o di e en azides appended wi h pola and non-pola chains, na u al p oduc s such as bio in, amino acids such as phenylalanine and pep ide nucleic acid (PNAs) monome s such as hymine. All compounds we e ob ained wi h high yields and sho eac ion imes unde mild condi ions, and he comple e cha ac e iza ion o all new de i a i es is also epo ed. COMMUNICATION Jou nal Name 2 | J. Name., 2012, 00, 1-3 This jou nal is © The Royal Socie y o Chemis y 20xx Please do no adjus ma gins Please do no adjus ma gins Scheme 1 Syn hesis o compound 5. Reagen s and condi ions: (i) C60, DBU, CB 4, ODCB, , 72h (50%); (ii) H2, Pd-C, DCM/MeOH, , o e nigh (100%); (iii) DPTS, DCC, DCM/DMF, , o e nigh (99%). The syn hesis o compound 5 by di ec Bingel addi ion o he co esponding cyclooc yne subs i u ed malona e unde he condi ions epo ed by Sun12 o he p epa a ion o hexakis adduc s o C60 yielded a complex mix u e o compounds whe e he b omina ion o he alkyne moie y was obse ed. The e o e, we decided o ollow a syn he ic s a egy in h ee s eps, as depic ed in Scheme 1. Malona e 1 (12 equi .) was added o C60 (1 equi .) in he p esence o DBU (20 equi .) and CB 4 (100 equi .) in ODCB a oom empe a u e. A e 72 h, hexakis adduc 2 was ob ained in 50% yield a e column ch oma og aphy. Dep o ec ion o he hyd oxyl g oups was ca ied ou by hyd ogena ion a a mosphe ic p essu e, yielding compound 3 in quan i a i e yield. Finally, he es e i ica ion o cyclooc yne ca boxylic acid 4 (see SI o syn he ic de ails) wi h hexakis adduc 3 using DCC/DPTS led o compound 5 in a quan i a i e yield, which was pu i ied by size-exclusion ch oma og aphy employing Sephadex. Compound 5 was comple ely cha ac e ized by he usual analy ical and spec oscopic echniques. The 13C NMR spec um con ains only h ee signals o he C60 ca bons, wo o he Csp2 a δ  145.8, 141.05 and one o he Csp3 a δ  69.1 (see ESI). Two di e en ca bonylic signals o he succinic and he malona e appea espec i ely a δ  172.2 and 163.6 and he Csp o he alkyne a e obse ed a 110.1 and 92.8 o he ca bons d and c o he cyclooc yne moie y, espec i ely (see Figu e 1). The abili y o compound 5 o be clicked o di e en azides was es ed wi h compounds 6a-e (Scheme 2). The addi ion eac ions we e ca ied ou in DMSO unde mic owa e i adia ion a 50ºC du ing 30 min. Compounds 7a-e (ob ained espec i ely om 6a-e ) we e pu i ied by size-exclusion ch oma og aphy using Sephadex (see ESI). The yields ob ained we e o e 90% in all cases. Jou nal Name COMMUNICATION This jou nal is © The Royal Socie y o Chemis y 20xx J. Name., 2013, 00, 1-3 | 3 Please do no adjus ma gins Please do no adjus ma gins Scheme 2. Syn hesis o clicked adduc s 7a-e. Reagen s and condi ions: (i) DMSO, 50°C unde MW, 30 min (93-99%). The wo possible egioisome s a e ep esen ed a he bo om. Cycloadduc s 7a-e we e ully cha ac e ized by FTIR, 1H and 13C NMR and MS and he assignmen o he signals in NMR was elucida ed by COSY and HSQC NMR spec oscopies (see suppo ing in o ma ion). The lack o he ypical band o he azide g oup in he FTIR spec a (  2100 cm-1) o he clicked adduc s was indica i e o he absence o un eac ed azide a e pu i ica ion. 1H NMR spec a show wo di e en signals o he CH o he cyclooc yne adjacen o iazole moie y (i.e. δ  4.82 and 4.69 o 7a ). Se e al o he signals appea duplica ed, indica ing he p esence o he wo expec ed egioisome s (see Scheme 2). Once assigned he signals o he 1H and 13C spec a using COSY and HSQC expe imen s (see ESI), he a io o egioisome s was calcula ed by in eg a ion o he signals in he 1H NMR spec um. Fo all he compounds, almos equal p opo ion o he wo isome s was ob ained ( 7a : 57% (A), 43% (B); 7b : 54% (A), 46% (B); 7c : 53% (A), 47% (B); 7d : 55% (A), 45% (B); 7e : 57% (A), 43% (B)), wi h a sligh excess o isome A, wi h less s e ic hind ance han isome B (see Figu e 1). This esul is compa able o p e ious s udies on monome ic compounds, indica ing ha he globula p esen a ion o cyclooc ynes p o ided by he hexakis adduc o C60 5 does no a ou he o ma ion o one egioisome o e he o he .17 13C NMR also shows he p esence o he wo possible egioisome s (see Figu e 1). Thus, while wo signals a e obse ed o he Csp2 o C60 o 7a-e (i.e.: 145.8 and 141.1 o 7a ), ou signals appea in he 13C NMR spec um o each compound co esponding o he wo ca bons o he iazole ing o he wo egioisome s (i.e.: 144.9, 144.8, 133.5 and 132.4 o 7a ). The es o he signals o he cyclooc yne moie y also appea duplica ed (see ESI). MS da a ob ained by MALDI-TOF spec ome y con i med he p esence o he molecula ion peak o 7a,b,e . Fo 7c-d , howe e , high le el o occu ing agmen a ion a oided he obse a ion o he expec ed molecula ion peaks. In conclusion, we ha e ca ied ou he syn hesis o a new building block o he syn hesis o hexakis adduc s o [60] ulle ene by using SPAAC. This compound is ob ained in h ee s eps by cyclop opana ion (Bingel eac ion), dep o ec ion and es e i ica ion, wi h e y good yields. The use o his building block was es ed in eac ions wi h a se ies o azides, leading o he clicked adduc s wi h yields o e 90%. Mos impo an ly, his me hodology a oids he use o coppe as a ca alys in he click cycloaddi ion eac ion, being o special in e es o he p epa a ion o globula ulle ene de i a i es o biological s udies. Figu e 1. 13 C NMR spec a o compounds 5 (up) and 7a (down) (CDCl 3 , 125.8 MHz). We hank inancial suppo by he Eu opean Resea ch Council (ERC- 320441-Chi alca bon), he Minis e io de Economía y Compe i i idad (MINECO) o Spain (p ojec s CTQ2014-52045-R and CTQ2014- 52328-P) and he Comunidad Au ónoma de Mad id (PHOTOCARBON p ojec S2013/MIT-2841). JRS hanks MINECO o a FPI ellowship and JJR acknowledges o CSIC o a JAEdoc con ac . No es and e e ences 1. A. Hi sch and O. Vos owsky, Eu . J. O g. Chem., 2001, 2001, 829-848. 2. S. Campidelli, T. 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