**4. Natural, semi-synthetic, and synthetic colchicines**

Many naturally occurring colchicine alkaloids (some of them are listed in **Figures 3** and **4**) have been converted into semi-synthetic compounds and have been prepared as potential antitumor agents. Usually starting with colchicine **1** hundreds of semi-synthetic and synthetic colchicine derivatives have been synthesized [28–30].

Starting compound was 1,2-*O*-didemethylcolchicine **16** converted into 1,2,3-*O*-tridemethyl colchiceine **17** [28–30], 1,2,3-*O*-tridemethyl-*N*-deacetylcolchiceine **18** [28–30], 1,2,3-*O*-tride methyl-*N*-deacetyl-*N*-trifluoroacetylcolchiceine **19** [28–30], and 1,2,3-*O*-tridemethyl-*N*-deace

**4.1. C-10 sulfur-containing derivatives**

NHR1

, or NR1

R2

lished that exchange of methoxyl substituent ─OCH3

**Figure 5.** Seminatural and synthetic thiocolchicines (chosen examples).

) and especially to methylthio (CH3

After many years of searching colchicine derivatives as good cytotoxic agents, it was estab-

ity. Thiocolchicine **31** is a colchicine **1** derivative used in the therapy of some diseases [43] and extensively studied in the field of oncological research as antimitotic agent [44–46]. There were mentioned some of wide range of synthesized colchicine compounds with thio substituent at C-10 position during last 60 years. Derivatives with alkylthio substituent at C-10 position have been synthesized from colchicine **31–35** (**Figure 5**) [47]. *N*-deacetyl-10-methylthiocolchicine **36** was converted into compounds: **37** [44], **38** and **39** [44]. 10-Methylthiocolchine was modified at C-3 position to compound 3-demethoxy-3-amino-10-methylthiocolchicine **40** and then to 3-demethoxy-3-glycosylaminothiocolchicines **41–47** (**Figure 5**) [48]. From derivatives **48**–**52**

at C-10 position to amino group (NH2

Cytotoxic Colchicine Alkaloids: From Plants to Drugs http://dx.doi.org/10.5772/intechopen.72622

S─) or alkylthio increases cytotoxic activ-

,

49

**Figure 3.** Naturally occurring colchicine derivatives (color version available on the online version).

tyl-*N*-formyl(2,4,6-trihydroxyphenyl)colchiceine **20** [28–30]. 1,2-didemethyl-*N*-deacetylcolchicine **21** was converted into: 1,2-didemethyl*-N*-deacetyl-*N*-(propane-2,3-diol)colchicine **22** [31] and 1,2-didemethyl-*N*-deacetyl-*N*-(propane-2,3-diacetyl)colchicine **23** [31]. Derivatives **24** with halogene substituent and with alkyl, aryl, or hydrogen **25** at C-10 position have also been obtained [32]. 10-demetoxy-10-azido-colchicine **26** [33] and 10-demetoxy-10-amino-colchicine = colchiceinamide **27** [34]. 2-Demethyl-*N*-benzyldemecolcine = speciocolchine **28** [35] has been prepared from 2-demethyldemecolcine. 10-*O*-p-tosylsulfonylcolchiceine **29** can be converted into compound **24** [36]. One of the interesting derivatives modified at C-7 position by –sulfur-containing substituent is *N*-deacetyl-*N*-(2merkaptoacetyl)-colchicine **30** (DAMAcolchicine) [37]. Glycopeptide dendrimer conjugates of colchicine modified at C-7 have been synthesized and tested as mitosis inhibitors [38]. *N*-substituted derivatives colchicine-lipids with different length of alkyl chain of olenyl and stearyl groups have been obtained and their interaction with lipid membrane has been studied [39]. Ring-C-modified colchicine analogs with different nitroso substituents in Diels-Alder reaction have been obtained [40]. 3-Demethyl derivative of colchicine and 10-metylthiocolchicine have been obtained also by regioselective bioconversion of **1** and **31** by microorganisms *Bacillus* IND-B 375 and stain of *Bacillus megaterium* ACBT03 [41, 42].

**Figure 4.** Natural, seminatural and synthetic colchicines (chosen examples).

#### **4.1. C-10 sulfur-containing derivatives**

tyl-*N*-formyl(2,4,6-trihydroxyphenyl)colchiceine **20** [28–30]. 1,2-didemethyl-*N*-deacetylcolchicine **21** was converted into: 1,2-didemethyl*-N*-deacetyl-*N*-(propane-2,3-diol)colchicine **22** [31] and 1,2-didemethyl-*N*-deacetyl-*N*-(propane-2,3-diacetyl)colchicine **23** [31]. Derivatives **24** with halogene substituent and with alkyl, aryl, or hydrogen **25** at C-10 position have also been obtained [32]. 10-demetoxy-10-azido-colchicine **26** [33] and 10-demetoxy-10-amino-colchicine = colchiceinamide **27** [34]. 2-Demethyl-*N*-benzyldemecolcine = speciocolchine **28** [35] has been prepared from 2-demethyldemecolcine. 10-*O*-p-tosylsulfonylcolchiceine **29** can be converted into compound **24** [36]. One of the interesting derivatives modified at C-7 position by –sulfur-containing substituent is *N*-deacetyl-*N*-(2merkaptoacetyl)-colchicine **30** (DAMAcolchicine) [37]. Glycopeptide dendrimer conjugates of colchicine modified at C-7 have been synthesized and tested as mitosis inhibitors [38]. *N*-substituted derivatives colchicine-lipids with different length of alkyl chain of olenyl and stearyl groups have been obtained and their interaction with lipid membrane has been studied [39]. Ring-C-modified colchicine analogs with different nitroso substituents in Diels-Alder reaction have been obtained [40]. 3-Demethyl derivative of colchicine and 10-metylthiocolchicine have been obtained also by regioselective bioconversion of **1** and **31** by microorganisms *Bacillus* IND-B 375 and stain of

**Figure 3.** Naturally occurring colchicine derivatives (color version available on the online version).

*Bacillus megaterium* ACBT03 [41, 42].

48 Cytotoxicity

**Figure 4.** Natural, seminatural and synthetic colchicines (chosen examples).

After many years of searching colchicine derivatives as good cytotoxic agents, it was established that exchange of methoxyl substituent ─OCH3 at C-10 position to amino group (NH2 , NHR1 , or NR1 R2 ) and especially to methylthio (CH3 S─) or alkylthio increases cytotoxic activity. Thiocolchicine **31** is a colchicine **1** derivative used in the therapy of some diseases [43] and extensively studied in the field of oncological research as antimitotic agent [44–46]. There were mentioned some of wide range of synthesized colchicine compounds with thio substituent at C-10 position during last 60 years. Derivatives with alkylthio substituent at C-10 position have been synthesized from colchicine **31–35** (**Figure 5**) [47]. *N*-deacetyl-10-methylthiocolchicine **36** was converted into compounds: **37** [44], **38** and **39** [44]. 10-Methylthiocolchine was modified at C-3 position to compound 3-demethoxy-3-amino-10-methylthiocolchicine **40** and then to 3-demethoxy-3-glycosylaminothiocolchicines **41–47** (**Figure 5**) [48]. From derivatives **48**–**52**

**Figure 5.** Seminatural and synthetic thiocolchicines (chosen examples).

esters of 1-*O*-demethyl, 2-*O*-demethyl and 3-*O*-demethylthiocolchicine were also obtained **53**– **57** (**Figure 5**) [49]. 10-methylthiocolchicine has been demethylated to 1-demethyl-10-methylthiocolchicine **58**, 2-demethyl-10-methylthiocolchicine **59**, and 1,2-*O*-didemethylthiocolchicine **52** then **58** and **59** have been oxidized to quinine (**Figure 6**) [50]. Complex ethers of 3-demethyl-10-methylthiocolchicine **62**–**65** have been prepared as potential pharmaceuticals [51]. The C-7 amide group of ring B with (*R*)-configuration [15] is also one of the crucial factors which decide of molecule's anticancer activity. Eight synthetic derivatives of *N*-deacetylthiocolchicine have been obtained and tested against cancer cell lines and 3 of them showed good activity **66**, **67**, **68** [52]. Thiocolchicine derivative **69** has been modified at C-2 carbon atom and then converted into salt **70** [53]. Among 37 thiocolchicine derivatives tested, compound **71** showed good activity as inhibitor of topoisomerases *in vitro* [54]. *N*-substituted thiocolchicine derivatives and their water-soluble phosphate salts **72–78** (and 5 others) have been obtained and their activity have been tested against cancer cell lines [55] (**Figure 7**).

From compound **79** acetamido ─NHCOCH3

obtained and their tubulin activity has been tested [58].

**5. Bioactivity of colchicine and its derivatives**

a colchicine-specific antigen-binding immunoglobulin [11].

replaced by ═CH2

ring B [59]**.**

structure.

such as colchicine.

cells [69].

substituent from C-7 has been removed and

Cytotoxic Colchicine Alkaloids: From Plants to Drugs http://dx.doi.org/10.5772/intechopen.72622 51

group [56]. Hybrids of vindoline, anhydrovinblastine, and vinorelbine

with thiocolchicine **31** podophyllotoxin and baccatinIII have been tested in arresting cell cycle and cytotoxic activity [57]. Series of thiocolchicine-podophyllotoxin conjugates have been

Compounds **80**, **81**, **82**, **83**, **84**, and **85** have been synthesized by four synthesis steps from colchicine **1** to thiocolchicine **31** then to 7-deacetylthiocolcicine **36** which has been converted into **80** and then to **81**, **82**, **83**, **84**, **85** and eight others which possess six-membered

Colchicine **1** has been known and used from ancient times, despite its toxicity to cure acute gout attacks because of its anti-inflammatory properties. After administration of colchicine **1,** it is mainly metabolized in liver *via* demethylation by cytochrome P450 system (isoform CYP 3A4) to 2-demethylcolchicine **2** and 3-demethylcolchicine **3** [11]. Colchiceine **12** was described as a metabolite in rats produced by cytochrome P450 3A4 isoform [60], but it does not occur in humans *in vivo* [61]. Colchicine's most common toxicity is gastrointestinal (nausea, vomiting, diarrhea, abdominal pain) which occurs during first 24 hours after overdose. Toxic effect of colchicine appears after oral administration of 7–60 mg of colchicine and is fatal, symptoms occur in about 4 h and death in about 4 days. Severe colchicine overdose may be treated with

Beside colchicine **1** has many naturally occurring derivatives many attempts have been made to discover more effective and less toxic analogs by modifying the substituents of its basic

Colchicine blocks mitosis metaphase due to different anti-mitotic effects: disruption of mitotic spindle formation and second disruption of the sol-gel formation. Colchicine can also interact with lipid membranes. The interaction between colchicine and membrane results with significant alternations of both the properties of the lipid membrane and alkaloid [39]. Tubulin is an α and β heterodimer initially identified as the cellular colchicine-tubulin protein [10, 62]. Colchicine can interact with human serum albumin, which has been studied by spectroscopic method [63, 64]. Study of colchicine-tubulin complex showed that colchicine binds at the location where it prevents curved tubulin from adopting a straight structure, which inhibits assembly. Microtubules are cytoskeletal polymers of tubulin involved in many cellular functions [65]. Their dynamic instability is controlled by many proteins and compounds

Colchicine and its biologically active derivatives, especially thiocolchicine and its derivatives, have been extensively tested on cancer cell lines for *in vitro* cytotoxicity, in mice, evaluated for inhibition of tubulin polymerization [66], on axonal cytoskeleton of rat peroneus nerve [67]. Thiocolchicine has been studied as a potent compound to treat Peyronie's disease [68]. Derivatives of thiocolchicine have been tested ex vivo to human T-lymphoblastoid (CEM)

**Figure 6.** Thiocolchicines with modified ring A: **60** 1,4-quinone and **61** quinomethane.

**Figure 7.** Thiocolchicines modified on ring B.

From compound **79** acetamido ─NHCOCH3 substituent from C-7 has been removed and replaced by ═CH2 group [56]. Hybrids of vindoline, anhydrovinblastine, and vinorelbine with thiocolchicine **31** podophyllotoxin and baccatinIII have been tested in arresting cell cycle and cytotoxic activity [57]. Series of thiocolchicine-podophyllotoxin conjugates have been obtained and their tubulin activity has been tested [58].

Compounds **80**, **81**, **82**, **83**, **84**, and **85** have been synthesized by four synthesis steps from colchicine **1** to thiocolchicine **31** then to 7-deacetylthiocolcicine **36** which has been converted into **80** and then to **81**, **82**, **83**, **84**, **85** and eight others which possess six-membered ring B [59]**.**
